Unity: Bake a NavMesh dynamically from multiple surfaces

BakeMultipleNavMesh.cs

GameObject[] walkableSurfaces = GameObject.FindGameObjectsWithTag("Floor");
CombineInstance[] objectsToCombine = new CombineInstance[walkableSurfaces.Length];

for (int i = 0; i < walkableSurfaces.Length; ++i)
{
    MeshFilter meshFilter = walkableSurfaces[i].GetComponent<MeshFilter>();

    // Extract mesh from each walkable surface (floor)
    objectsToCombine[i].mesh = meshFilter.sharedMesh;
    objectsToCombine[i].transform = meshFilter.transform.localToWorldMatrix;

    // Disable original single component
    walkableSurfaces[i].gameObject.SetActive(false);
}

// New GameObject to merge the floors
GameObject floor = GameObject.CreatePrimitive(PrimitiveType.Plane);

// Combine all meshes and set as the new mesh filter
floor.GetComponent<MeshFilter>().mesh = new Mesh();
floor.GetComponent<MeshFilter>().mesh.CombineMeshes(objectsToCombine);

// Update collider to fit all sub-components
MeshCollider meshCollider = floor.GetComponent<MeshCollider>();
meshCollider.sharedMesh = floor.GetComponent<MeshFilter>().mesh;

// Build dynamic NavMesh
NavMeshSurface surface = floor.AddComponent<NavMeshSurface>();
surface.BuildNavMesh();