20 gauge is what u want, some use 22, some use18 its all in preference, yes galvanized is zinc cotaed to keep it from rusting but it is NOT what u want to use for body repair. also u shouldnt need to go to a metal shop to get a peice of sheetmetal just go to your local auto body supplier ie. napa, carquest or whatever u have locally and get a sheet they normally come in 2'x3' and 3'x4'. and also galvanized can be welded without any problems ibn the catually welding process its just they do not reccomend inhaling alot of the fumes it makes when welding it. I made a custom tube bumper for my toyota out of galvanized pipe and didnt have any issues with welding it or the fumesit made.