Illustrator 3D (Extrude & Bevel)

I have been having a problem with the extrude & bevel feature in Illustrator CS2.

I work in an architectural studio, and I have been trying to extrude floorplans. However, when I have two groups of oblects - rooms & walkways - that I extrude, they don't intersect. The group of extruded rooms sits over the extruded walkway.

So, if I then group the two groups together, they intersect, but now I have no way to lower the "extrude depth" of each individual group.

The tutorial of a "3D Map" in Illustrator.,..
http://forum.teamphotoshop.com/showthread.php?t=24795
....shows this as pretty simple (buildings/roads vs rooms/walkways), but I must be missing a step...

Help?

I saw your other post in the "quick and dirty perspective" thread....

perhaps you could shoot Mihai a PM, since thats who wrote the tutorial I'll just bet that pixel peddler will know exactly whats happening.

you might also be able to contact Mihai from the http://roundpixel.org website.