Jonathan Ross (UK chat show host) has a retro room with an Amiga in it, I remember seeing it on the telly.
He did a great job with the deco, the walls were sort of cushioned and lined with brown suede-looking stuff. A bit like something out of the film Solaris (the original one)!
I'd go for a big rounded desk (or three straight desks arranged in a semi-circle) so I can in the middle and move around to the different machines, then have an area for each (commodore 8-bit, Amiga, PC, etc.)
Given a big-enough room I'd want an arcade cabinet or two, plus a pool table. Then I'd wake up and have my cornflakes.