I agree with Lugnutz on sticking with name brand. I originally bought a Campbell Hausfield flux core welder running on 120V, but upgraded when I got into my AD truck project to a Lincoln with MIG capabilities, which is what you want to use for sheet metal welding. A 120V machine will be fine for sheet metal, but if you ever want to weld something thicker, you'll be better served by one running on 240V with more power. The limit on 120V units is typically around 90A, which means multiple passes on thick stuff.
Setting up a new machine will cost you more than just the machine price, as you'll need a CO2 bottle, and want a cart for the whole deal, and a bunch of miscellaneous accessories like workpiece magnets, butt weld clamps (HF ones are cheap and work OK), a good (autodarkening) hood, and some good gloves. If you can find a used machine on CL with all that stuff, even better.
Before you start in on your patch panels, get some scrap sheet metal and PRACTICE, PRACTICE, PRACTICE. There are lots of YouTube videos that will help, but some are so-so and some are pure junk. Read the manual that comes with the machine a couple times so it sinks in.
Good Luck
P.S. If you run into trouble, PM Robert (username MP&C here on Stovebolt.com).
He's an expert and willing to help out. If you can find some of his threads on the GarageJournal, you can see some of his awesome metalworking skills.
