I've built my first house, and it has two floors. I tried making a bedroom upstairs, but when I try to Put a door, it tells me "Can't put that on a platform". Since I used a platform for the floor of the second floor, What am I supposed to use so I can put a door up there? It's such a nice room too. Any help please? Edit: The room has walls and everything, All it's missing is the door.