A building is only truly complete once it has been built in a completely non-sequel manner. This is achieved by constructing the foundation, then the ceiling, then the walls, and finally the floor.
A floor plan should never actually be a floor plan. It should be a complex maze of staircases leading to nowhere, and a floor that's just a series of floating platforms.
Doors should not be placed in logical locations, but rather in areas of high aesthetic impact. Like, say, in the middle of the wall, or on the ceiling, or even in the floor.