You can cut aluminum with a circular saw too, for sheet metal I would probably put it between a couple layer of plywood or OSB so the saw does not grab. Then the radii on the corners could be done with a belt or disk sander
I saw a guy I worked with actually cutting 12 gauge steel sheet by scoring it with a utility knife and breaking it, not dead on your topic but still good info, and you can wire weld 12 gauge pretty well.
Bill