...swapping floor & ceiling textures, and inverting the walls textures would give you the fastest upside down appearance to your room.
Run the textures (
orientated the way you want them) through a third party application, and create a unique set of segments. This way, you'd have a ready-to-use arsenal of segments.
Doors and windows would take a little bit of refinement, but it could be possible to create an upside down set of these as well.
Could be a fun project, and is very possible to do.
Widow 13 - Coming Spring 2008