All you need is some photocopy boxes, a colour printer and sticky-tape/glue.
I found the wall patterns on the web. I don't have the link here at home with me but when I get to work I will post the credit.
We have an A3 box as Autobot HQ (mine - used glue) and A4 box Autobot and Decepticon HQs (the kids' - used stickytape. theirs is likely to have more wear and tear).
uh.....oops
Edit: here's the links from the author: http://forums.tformers.com/talk/inde...howtopic=91920
and the index: http://x4.ofgraphicdesign.com/projects/ark/