RandhirP inside BuildingController.cs, add a callback to rebuild the exterior walls and roof:

Then a bit below, where you see "if (rooms.Length < 1) return", then that too:
if (rooms.Length < 1)
{
proceduralBuilding.Clear(true, true, true);
proceduralRoof.Clear(true, true, true);
return;
}
in FloorController_prefab, make sure all the references are not missing:
