This was made out of scrap from a fence I took down. It's 1 1/2 square, about 14 ga I'd guess, a handle made from 1" pipe and some scrap angle.
The bottom is 1/2" sq tubing to support plywood with sheets of aluminum over the plywood.
I see a lot of welders on the upper shelf of carts like this, but I like the lower center of gravity, the welder is a little more protected from things bumping into it, and there's not much handier than a shelf near a welder for the odds and ends (tips, cutters, spray, misc parts, and so on).
Yeah, it's Blue, but I'm here to see about adding some Green to the shop.