Frame Fab Help

[nightfer]

I have to fab a frame for a small powder coating oven (about 20 feet long, 6 feet high, 6 feet wide) out of 2x2 square tubing. I made a rough drawing below of the side view and then below it the top view. From the side you can see that the legs are not attached to anything at the bottom. I was thinking the best way to go would be to build the whole thing upside down and then flip it. Any other ideas?