diff --git a/apps/editor/components/tools/slab/slab-tool.tsx b/apps/editor/components/tools/slab/slab-tool.tsx
new file mode 100644
index 00000000..65da1879
--- /dev/null
+++ b/apps/editor/components/tools/slab/slab-tool.tsx
@@ -0,0 +1,364 @@
+import { emitter, type GridEvent, useScene, SlabNode, type LevelNode } from "@pascal-app/core";
+import { useViewer } from "@pascal-app/viewer";
+import { useEffect, useMemo, useRef, useState } from "react";
+import { BufferGeometry, DoubleSide, type Line, type Mesh, Shape, Vector3 } from "three";
+import useEditor from "@/store/use-editor";
+
+const Y_OFFSET = 0.02;
+
+/**
+ * Snaps a point to the nearest axis-aligned or 45-degree diagonal from the last point
+ */
+const calculateSnapPoint = (
+  lastPoint: [number, number],
+  currentPoint: [number, number]
+): [number, number] => {
+  const [x1, y1] = lastPoint;
+  const [x, y] = currentPoint;
+
+  const dx = x - x1;
+  const dy = y - y1;
+  const absDx = Math.abs(dx);
+  const absDy = Math.abs(dy);
+
+  // Calculate distances to horizontal, vertical, and diagonal lines
+  const horizontalDist = absDy;
+  const verticalDist = absDx;
+  const diagonalDist = Math.abs(absDx - absDy);
+
+  // Find the minimum distance to determine which axis to snap to
+  const minDist = Math.min(horizontalDist, verticalDist, diagonalDist);
+
+  if (minDist === diagonalDist) {
+    // Snap to 45° diagonal
+    const diagonalLength = Math.min(absDx, absDy);
+    return [
+      x1 + Math.sign(dx) * diagonalLength,
+      y1 + Math.sign(dy) * diagonalLength,
+    ];
+  } else if (minDist === horizontalDist) {
+    // Snap to horizontal
+    return [x, y1];
+  } else {
+    // Snap to vertical
+    return [x1, y];
+  }
+};
+
+/**
+ * Creates a slab with the given polygon points
+ */
+const commitSlabDrawing = (
+  levelId: LevelNode["id"],
+  points: Array<[number, number]>
+) => {
+  const { createNode, nodes } = useScene.getState();
+
+  // Count existing slabs for naming
+  const slabCount = Object.values(nodes).filter((n) => n.type === "slab").length;
+  const name = `Slab ${slabCount + 1}`;
+
+  const slab = SlabNode.parse({
+    name,
+    polygon: points,
+  });
+
+  createNode(slab, levelId);
+};
+
+type PreviewState = {
+  points: Array<[number, number]>;
+  cursorPoint: [number, number] | null;
+};
+
+// Helper to validate point values (no NaN or Infinity)
+const isValidPoint = (
+  pt: [number, number] | null | undefined
+): pt is [number, number] => {
+  if (!pt) return false;
+  return Number.isFinite(pt[0]) && Number.isFinite(pt[1]);
+};
+
+export const SlabTool: React.FC = () => {
+  const cursorRef = useRef<Mesh>(null);
+  const mainLineRef = useRef<Line>(null!);
+  const closingLineRef = useRef<Line>(null!);
+  const pointsRef = useRef<Array<[number, number]>>([]);
+  const currentLevelId = useViewer((state) => state.selection.levelId);
+  const setTool = useEditor((state) => state.setTool);
+
+  // Preview state for reactive rendering (for shape and point markers)
+  const [preview, setPreview] = useState<PreviewState>({
+    points: [],
+    cursorPoint: null,
+  });
+
+  useEffect(() => {
+    if (!currentLevelId) return;
+
+    let cursorPosition: [number, number] = [0, 0];
+
+    // Initialize line geometries
+    mainLineRef.current.geometry = new BufferGeometry();
+    closingLineRef.current.geometry = new BufferGeometry();
+
+    const updateLines = () => {
+      const points = pointsRef.current;
+
+      if (points.length === 0) {
+        mainLineRef.current.visible = false;
+        closingLineRef.current.visible = false;
+        return;
+      }
+
+      // Build main line points
+      const linePoints: Vector3[] = points.map(
+        ([x, z]) => new Vector3(x, Y_OFFSET, z)
+      );
+
+      // Add cursor point
+      const lastPoint = points[points.length - 1];
+      if (lastPoint) {
+        const snapped = calculateSnapPoint(lastPoint, cursorPosition);
+        if (isValidPoint(snapped)) {
+          linePoints.push(new Vector3(snapped[0], Y_OFFSET, snapped[1]));
+        }
+      }
+
+      // Update main line geometry
+      if (linePoints.length >= 2) {
+        mainLineRef.current.geometry.dispose();
+        mainLineRef.current.geometry = new BufferGeometry().setFromPoints(linePoints);
+        mainLineRef.current.visible = true;
+      } else {
+        mainLineRef.current.visible = false;
+      }
+
+      // Update closing line (from cursor back to first point)
+      const firstPoint = points[0];
+      if (points.length >= 2 && lastPoint && isValidPoint(firstPoint)) {
+        const snapped = calculateSnapPoint(lastPoint, cursorPosition);
+        if (isValidPoint(snapped)) {
+          const closingPoints = [
+            new Vector3(snapped[0], Y_OFFSET, snapped[1]),
+            new Vector3(firstPoint[0], Y_OFFSET, firstPoint[1]),
+          ];
+          closingLineRef.current.geometry.dispose();
+          closingLineRef.current.geometry = new BufferGeometry().setFromPoints(closingPoints);
+          closingLineRef.current.visible = true;
+        }
+      } else {
+        closingLineRef.current.visible = false;
+      }
+    };
+
+    const updatePreview = () => {
+      const points = pointsRef.current;
+      const lastPoint = points[points.length - 1];
+
+      let cursorPt: [number, number] | null = null;
+      if (lastPoint) {
+        cursorPt = calculateSnapPoint(lastPoint, cursorPosition);
+      } else if (points.length === 0) {
+        cursorPt = cursorPosition;
+      }
+
+      setPreview({ points: [...points], cursorPoint: cursorPt });
+      updateLines();
+    };
+
+    const onGridMove = (event: GridEvent) => {
+      if (!cursorRef.current) return;
+
+      // Snap to 0.5 grid
+      const gridX = Math.round(event.position[0] * 2) / 2;
+      const gridZ = Math.round(event.position[2] * 2) / 2;
+      cursorPosition = [gridX, gridZ];
+
+      // If we have points, snap to axis from last point
+      const lastPoint = pointsRef.current[pointsRef.current.length - 1];
+      if (lastPoint) {
+        const snapped = calculateSnapPoint(lastPoint, cursorPosition);
+        cursorRef.current.position.set(snapped[0], event.position[1], snapped[1]);
+      } else {
+        cursorRef.current.position.set(gridX, event.position[1], gridZ);
+      }
+
+      updatePreview();
+    };
+
+    const onGridClick = (event: GridEvent) => {
+      if (!currentLevelId) return;
+
+      const gridX = Math.round(event.position[0] * 2) / 2;
+      const gridZ = Math.round(event.position[2] * 2) / 2;
+      let clickPoint: [number, number] = [gridX, gridZ];
+
+      // Snap to axis from last point
+      const lastPoint = pointsRef.current[pointsRef.current.length - 1];
+      if (lastPoint) {
+        clickPoint = calculateSnapPoint(lastPoint, clickPoint);
+      }
+
+      // Check if clicking on the first point to close the shape
+      const firstPoint = pointsRef.current[0];
+      if (
+        pointsRef.current.length >= 3 &&
+        firstPoint &&
+        Math.abs(clickPoint[0] - firstPoint[0]) < 0.25 &&
+        Math.abs(clickPoint[1] - firstPoint[1]) < 0.25
+      ) {
+        // Create the slab
+        commitSlabDrawing(currentLevelId, pointsRef.current);
+
+        // Reset state
+        pointsRef.current = [];
+        setPreview({ points: [], cursorPoint: null });
+        mainLineRef.current.visible = false;
+        closingLineRef.current.visible = false;
+
+        // Deactivate tool
+        setTool(null);
+      } else {
+        // Add point to polygon
+        pointsRef.current = [...pointsRef.current, clickPoint];
+        updatePreview();
+      }
+    };
+
+    const onGridDoubleClick = (_event: GridEvent) => {
+      if (!currentLevelId) return;
+
+      // Need at least 3 points to form a polygon
+      if (pointsRef.current.length >= 3) {
+        commitSlabDrawing(currentLevelId, pointsRef.current);
+
+        // Reset state
+        pointsRef.current = [];
+        setPreview({ points: [], cursorPoint: null });
+        mainLineRef.current.visible = false;
+        closingLineRef.current.visible = false;
+
+        // Deactivate tool
+        setTool(null);
+      }
+    };
+
+    // Subscribe to events
+    emitter.on("grid:move", onGridMove);
+    emitter.on("grid:click", onGridClick);
+    emitter.on("grid:double-click", onGridDoubleClick);
+
+    return () => {
+      emitter.off("grid:move", onGridMove);
+      emitter.off("grid:click", onGridClick);
+      emitter.off("grid:double-click", onGridDoubleClick);
+
+      // Reset state on unmount
+      pointsRef.current = [];
+    };
+  }, [currentLevelId, setTool]);
+
+  const { points, cursorPoint } = preview;
+
+  // Create preview shape when we have 3+ points
+  const previewShape = useMemo(() => {
+    if (points.length < 3) return null;
+
+    const allPoints = [...points];
+    if (isValidPoint(cursorPoint)) {
+      allPoints.push(cursorPoint);
+    }
+
+    // THREE.Shape is in X-Y plane. After rotation of -PI/2 around X:
+    // - Shape X -> World X
+    // - Shape Y -> World -Z (so we negate Z to get correct orientation)
+    const firstPt = allPoints[0];
+    if (!isValidPoint(firstPt)) return null;
+
+    const shape = new Shape();
+    shape.moveTo(firstPt[0], -firstPt[1]);
+
+    for (let i = 1; i < allPoints.length; i++) {
+      const pt = allPoints[i];
+      if (isValidPoint(pt)) {
+        shape.lineTo(pt[0], -pt[1]);
+      }
+    }
+    shape.closePath();
+
+    return shape;
+  }, [points, cursorPoint]);
+
+  return (
+    <group>
+      {/* Cursor */}
+      <mesh ref={cursorRef}>
+        <sphereGeometry args={[0.1, 16, 16]} />
+        <meshBasicMaterial
+          color="#a3a3a3"
+          depthTest={false}
+          depthWrite={false}
+        />
+      </mesh>
+
+      {/* Preview fill */}
+      {previewShape && (
+        <mesh
+          frustumCulled={false}
+          position={[0, Y_OFFSET, 0]}
+          rotation={[-Math.PI / 2, 0, 0]}
+        >
+          <shapeGeometry args={[previewShape]} />
+          <meshBasicMaterial
+            color="#a3a3a3"
+            depthTest={false}
+            opacity={0.3}
+            side={DoubleSide}
+            transparent
+          />
+        </mesh>
+      )}
+
+      {/* Main line - uses native line element with TSL-compatible material */}
+      {/* @ts-ignore */}
+      <line ref={mainLineRef} frustumCulled={false} renderOrder={1} visible={false}>
+        <bufferGeometry />
+        <lineBasicNodeMaterial
+          color="#737373"
+          linewidth={3}
+          depthTest={false}
+          depthWrite={false}
+        />
+      </line>
+
+      {/* Closing line - uses native line element with TSL-compatible material */}
+      {/* @ts-ignore */}
+      <line ref={closingLineRef} frustumCulled={false} renderOrder={1} visible={false}>
+        <bufferGeometry />
+        <lineBasicNodeMaterial
+          color="#737373"
+          linewidth={2}
+          depthTest={false}
+          depthWrite={false}
+          opacity={0.5}
+          transparent
+        />
+      </line>
+
+      {/* Point markers */}
+      {points.map(([x, z], index) =>
+        isValidPoint([x, z]) ? (
+          <mesh key={index} position={[x, Y_OFFSET + 0.01, z]}>
+            <sphereGeometry args={[0.1, 16, 16]} />
+            <meshBasicMaterial
+              color={index === 0 ? "#22c55e" : "#a3a3a3"}
+              depthTest={false}
+              depthWrite={false}
+            />
+          </mesh>
+        ) : null
+      )}
+    </group>
+  );
+};
diff --git a/apps/editor/components/tools/tool-manager.tsx b/apps/editor/components/tools/tool-manager.tsx
index 914f2a48..5c023bf8 100644
--- a/apps/editor/components/tools/tool-manager.tsx
+++ b/apps/editor/components/tools/tool-manager.tsx
@@ -1,6 +1,7 @@
 import useEditor, { type Phase, type Tool } from "@/store/use-editor";
 import { useViewer } from "@pascal-app/viewer";
 import { ItemTool } from "./item/item-tool";
+import { SlabTool } from "./slab/slab-tool";
 import { WallTool } from "./wall/wall-tool";
 import { ZoneBoundaryEditor } from "./zone/zone-boundary-editor";
 import { ZoneTool } from "./zone/zone-tool";
@@ -9,6 +10,7 @@ const tools: Record<Phase, Partial<Record<Tool, React.FC>>> = {
   site: {},
   structure: {
     wall: WallTool,
+    slab: SlabTool,
     item: ItemTool,
     zone: ZoneTool,
   },
diff --git a/packages/core/src/index.ts b/packages/core/src/index.ts
index 12648883..8dc560f9 100644
--- a/packages/core/src/index.ts
+++ b/packages/core/src/index.ts
@@ -26,6 +26,7 @@ export { useSpatialQuery } from './hooks/spatial-grid/use-spatial-query'
 export * from './schema'
 export { default as useScene } from './store/use-scene'
 // Systems
+export { SlabSystem } from './systems/slab/slab-system'
 export { WallSystem } from './systems/wall/wall-system'
 
 export { isObject } from './utils/types'
diff --git a/packages/core/src/systems/slab/slab-system.tsx b/packages/core/src/systems/slab/slab-system.tsx
new file mode 100644
index 00000000..1240ab8a
--- /dev/null
+++ b/packages/core/src/systems/slab/slab-system.tsx
@@ -0,0 +1,79 @@
+import { useFrame } from '@react-three/fiber'
+import * as THREE from 'three'
+import { sceneRegistry } from '../../hooks/scene-registry/scene-registry'
+import type { AnyNodeId, SlabNode } from '../../schema'
+import useScene from '../../store/use-scene'
+
+// ============================================================================
+// SLAB SYSTEM
+// ============================================================================
+
+export const SlabSystem = () => {
+  const { nodes, dirtyNodes, clearDirty } = useScene()
+
+  useFrame(() => {
+    if (dirtyNodes.size === 0) return
+
+    // Process dirty slabs
+    dirtyNodes.forEach((id) => {
+      const node = nodes[id]
+      if (!node || node.type !== 'slab') return
+
+      const mesh = sceneRegistry.nodes.get(id) as THREE.Mesh
+      if (mesh) {
+        updateSlabGeometry(node as SlabNode, mesh)
+      }
+      clearDirty(id as AnyNodeId)
+    })
+  })
+
+  return null
+}
+
+/**
+ * Updates the geometry for a single slab
+ */
+function updateSlabGeometry(node: SlabNode, mesh: THREE.Mesh) {
+  const newGeo = generateSlabGeometry(node)
+
+  mesh.geometry.dispose()
+  mesh.geometry = newGeo
+}
+
+/**
+ * Generates extruded slab geometry from polygon
+ */
+export function generateSlabGeometry(slabNode: SlabNode): THREE.BufferGeometry {
+  const polygon = slabNode.polygon
+  const elevation = slabNode.elevation ?? 0.05
+
+  if (polygon.length < 3) {
+    return new THREE.BufferGeometry()
+  }
+
+  // Create shape from polygon
+  // Shape is in X-Y plane, we'll rotate to X-Z plane after extrusion
+  const shape = new THREE.Shape()
+  const firstPt = polygon[0]!
+
+  // Negate Y (which becomes Z) to get correct orientation after rotation
+  shape.moveTo(firstPt[0], -firstPt[1])
+
+  for (let i = 1; i < polygon.length; i++) {
+    const pt = polygon[i]!
+    shape.lineTo(pt[0], -pt[1])
+  }
+  shape.closePath()
+
+  // Extrude the shape by elevation
+  const geometry = new THREE.ExtrudeGeometry(shape, {
+    depth: elevation,
+    bevelEnabled: false,
+  })
+
+  // Rotate so extrusion direction (Z) becomes height direction (Y)
+  geometry.rotateX(-Math.PI / 2)
+  geometry.computeVertexNormals()
+
+  return geometry
+}
diff --git a/packages/viewer/src/components/renderers/node-renderer.tsx b/packages/viewer/src/components/renderers/node-renderer.tsx
index 54fdec91..7ff8a7a6 100644
--- a/packages/viewer/src/components/renderers/node-renderer.tsx
+++ b/packages/viewer/src/components/renderers/node-renderer.tsx
@@ -4,6 +4,7 @@ import { type AnyNode, useScene } from '@pascal-app/core'
 import { BuildingRenderer } from './building/building-renderer'
 import { ItemRenderer } from './item/item-renderer'
 import { LevelRenderer } from './level/level-renderer'
+import { SlabRenderer } from './slab/slab-renderer'
 import { WallRenderer } from './wall/wall-renderer'
 import { ZoneRenderer } from './zone/zone-renderer'
 
@@ -17,6 +18,7 @@ export const NodeRenderer = ({ nodeId }: { nodeId: AnyNode['id'] }) => {
       {node.type === 'building' && <BuildingRenderer node={node} />}
       {node.type === 'level' && <LevelRenderer node={node} />}
       {node.type === 'item' && <ItemRenderer node={node} />}
+      {node.type === 'slab' && <SlabRenderer node={node} />}
       {node.type === 'wall' && <WallRenderer node={node} />}
       {node.type === 'zone' && <ZoneRenderer node={node} />}
     </>
diff --git a/packages/viewer/src/components/renderers/slab/slab-renderer.tsx b/packages/viewer/src/components/renderers/slab/slab-renderer.tsx
new file mode 100644
index 00000000..96390272
--- /dev/null
+++ b/packages/viewer/src/components/renderers/slab/slab-renderer.tsx
@@ -0,0 +1,17 @@
+import { useRegistry, type SlabNode } from '@pascal-app/core'
+import { useRef } from 'react'
+import type { Mesh } from 'three'
+
+export const SlabRenderer = ({ node }: { node: SlabNode }) => {
+  const ref = useRef<Mesh>(null!)
+
+  useRegistry(node.id, 'slab', ref)
+
+  return (
+    <mesh ref={ref} castShadow receiveShadow>
+      {/* SlabSystem will replace this geometry in the next frame */}
+      <boxGeometry args={[0, 0, 0]} />
+      <meshStandardMaterial color="#e5e5e5" />
+    </mesh>
+  )
+}
diff --git a/packages/viewer/src/components/viewer/index.tsx b/packages/viewer/src/components/viewer/index.tsx
index 760c2df7..363f21ba 100644
--- a/packages/viewer/src/components/viewer/index.tsx
+++ b/packages/viewer/src/components/viewer/index.tsx
@@ -1,6 +1,6 @@
 'use client'
 
-import { WallSystem } from '@pascal-app/core'
+import { SlabSystem, WallSystem } from '@pascal-app/core'
 import { Bvh, Environment } from '@react-three/drei'
 import { Canvas, extend, type ThreeToJSXElements } from '@react-three/fiber'
 import * as THREE from 'three/webgpu'
@@ -40,6 +40,7 @@ const Viewer: React.FC<ViewerProps> = ({ children }) => {
 
       {/* Default Systems */}
       <LevelSystem />
+      <SlabSystem />
       <WallSystem />
       <PostProcessing />