A-frame welded on, welded corner uprights onto frame, and welded center brace. If you look on the rear uprights, you'll see a piece of thinner wall angle, this is going to be the top of the frame.
I've not decided yet what to make the walls out of, thinking some 1x6 or so pressure treated boards. I think maybe lining the metal with the same material that I used on the bumpers, in black, and a grey version on the boards. Thoughts?