Considering the new Lua Scripting language this would be easy to implement, you'd simply need to create a house, name the object whatever you'd like, find out the function to hide a game object, and simply hide the interior underneath the gameobject, make the door interactable, so when you interact with it the script fires, hides the gameobject and kablam, interior. When i find out the function names i'll make a tutorial on it.