I wish I had the wall space for one, as well... but I have stared reading a handyman how to book called Shop Notes, and I got hold of some back issues, and they show how to build a couple of different styles of panel saws.
The one that I was goign to originally build, instead of sliding the material thru the stationary saw, the material is stationary, and the panel saw moves horizontally (it is in issue #88)...
But the one that I have decided to build instead of a sliding track system, it has grooves in each side as well as top and bottom, and there is a guide rail that the saw moves across. It is built from 1" x 4"s in a grid pattern to support the material, and it folds flat against the wall.