I would split each building into 3 part types,
1
Exterior base
exterior level
exterior roof
2
Interior layout.
3
Interior auto-floor.

Use say 1-5 exterior bases - First floor from outside - inlcude reverse walls.
Each ex base has 1-5 level version - second-xth floors from outside, with reverses inside walls.
- And 1-5 roof versions.

Then move inside and drop in 1-5 inside layouts, inner walls, rooms, chairs, beds ect.. Each inside level will not have a floor/ceiling.
The base ex provides a floor plane. But each interior auto creates a two sided ceiling/floor plan for the level about(even if only one level building)
The auto floor/ceiling should have 1-5 version that can be change by value or flag and also if wanted 1-5 textures that can be changed this way .


Drop a base ex... Select it's look. Drop in a interior layout select it's style, gen a auto ceiling/floor pick it's style and texture. If wish drop a second level ex , and drop in and other level interior... When done cap with a roof...

One final note for workflow to production. It would be great if the work done in the editor was exported out into one model structure file, that could be loaded in the production game. This way all the configuration is in the editor and the product doesn't need the extra bits and options. Finally, Through a model in parts -> I believe -> hit.chuck values can with vmask to allow visibility into the building as if setting separate entities to alpha 0..