However! If you don't mind this workaround, it might allow you to start 'texturing' your models - Go into blender and on each model, create new Material slots (woodenPK, metalPK, stonePK, GlassPK) Then, if you look at your particular UV map for the blender file, you'll see that some of the model takes up a section of the UV. Grab up each section of the model, and ASSIGN those vertices to that particular material. Then save as OBJ file. If you use a uniform format for the materials of each structure model, you SHOULD be able to affect each one. ALSO!!!!
I have found that importing each model into Blender as 1.2 scale makes each wall approximately 3 units. This makes things a bit easier to work with for me and the gridding.