I like Ken's table frame, very simple and sturdy. I want to add for the leveling, you can buy adjustable furniture feet at Home Depot (Lowe's, Rona, etc.) that you drill a hole into your leg (or support frame or whatever) and then a threaded socket goes into the hole and a threaded foot screws into the socket. Use about 6-8 of these around Ken's frame (with the feet pointing up to support the top) and you can perfectly level and support whatever building surface you choose to use. They are infinitely adjustable and allow you to re-true everything as often as you want in only a few minutes.

Mark