Well, you could do this.

But to be honest, you're going about this in a silly way. AddWall(), AddFloor() and so on are meant as quick demo'ing functions. They're not meant for level designing. Use a modeller
or write your own level editing tools in which you implement correct functionality. Hybrid is easier of course, create a level editing tool which imports props and map sections that you modelled outside in max. A lot of games take the hybrid approach, Fallout springs to mind.