Stew,
If it's the sort of thing you are considering, the current (April 2012, no 188) copy of MEW has a description of a home-made bead roller in it. The throat depth is 490mm. No drawings, but the photos and description are self-explanatory. The author doesn't say what gauge of steel it will handle. He shows a repair panel he made for a Triumph Spitfire, but if IIRC the body panels on the Spitfire my wife owned 35 years ago were pretty thin.
Andy