First, if you go to the backpacking.net home page, on the left hand side there is a link for "make your own gear" section that has some plans on making your own tent.

I have used two of the same tents you are getting from Tom. I agree, three adults max and really two if you want to have good room for gear inside.

If you are going to make custom tents I think your best bet will be to break down the tent body and rain fly into flat sheets and build from there. Since the existing tent shape uses all flat panels you should get plenty of material to work with.

You may find, like I did, that among the group of tents you get there are some that look almost new, and some that look about ready for the scrap pile. So far I have been happy to use the newer ones as is for family car camping.