Well, my next project will be based off square steel. If you can weld & have a chopsaw your set!
I borrowed a racing seat out of my baja bug to build a frame around. To start it, I just layed the pedals out and sat down in teh chair, and went from there. I estimated how & where the wheel needed to be. What wheel are you using? Mines built for the DFP. Im 5'6". The length of the frame from the front of the seat (where the tabs are mounted & seats bolted) to where the heel of my foot would be, and the pedal platform is mounted, is 18". The length is 30" to the end of the frame. The width for stability was only ~ 20" wide total. I gave the pedals just about a 3" lift up front, since I was sittin pretty much on the floor.
keep in mind you want a slant for the "table mount". The wheel is designed for the player to be sitting high and using a flat table. You need to counter that when you build your cockpit. When I actually began building it, everything came down to eyeballing it. measurements were altered if i felt it was needed. Its not perfect, but its pretty damn nice!
Hope this helped! Feel free if you have any more questions
Mike