Thanks for all the insight guys, you've been a big help.

18ga seems more than sufficient especially if the floor plans are 18ga. But 16ga is food for thought, you make a good point as far as more material to work with. I can tig so welding isn't a problem, I just don't want any cracks 2 years after I get it painted.
Is 16ga a lot harder to work with as far as forming corners?

Thanks again guys.

Kevin