Yeah forget lowes. Got to a local metal/steel supplier. It is so much cheaper. Just get a 1/2 or 1/4 sheet of 16, 18 and 20 gauge sheet metal. 16 is only for more structural areas. Get yourself a sheetmetal thickness gauge with the slots in it and see what you need.
It really is cheaper at a metal supply house. You can get a 1/2 sheet 4' x 4' for what you'd pay for a tiny piece at Lowes or HD.
Wes