1st, Awesome thread for an incredible theater. I spent pretty much all night reading the whole thing, and I am seriously envious here. Wow. I think it's better than the one that guy built in his garage. You know, the red and black one?
2nd, Would it be possible to post the google sketchup file? I just tried my hand at drafting out a basement floor plan with sketchup and it's really easy to do. That program is so cool. You are absolutely right about starting with the floorplan and then raising into 3D. I learned that the hard way. Your basement is very similar to ours and it would be a handy reference. Either way, good job start to finish.