I don't mean to hijack, but I never posted the one I made a while back.
Just some scrap 1/4" diamond sheet metal I had laying around.
My Grandfather had gave my mom some homemade clothes poles many years back, and she no longer used them.... So I figured I'd incorporate them in as well for a little extra

He used 2" Square tubing, 1/8" wall. I also used it for the hitch!
edit; I forgot, there's also 1 1/2" x 1/4" flat stock running underneath the square and around the side for extra support.
36"x48" with 36" tall sides.
Never found anything it couldn't hold yet.
Just using cheap HF rims, I think they're 400lb cap.
Flattened them like a pancake many, many times... but still function as intended

It's actually using 4 400lb tires, with a little pivot device so that no weight is on the mower, and it can pivot depending on terrain.
But it still is fixed, so that it can move forward/backup just like normal.
I almost wish I just took the time to make it with a ball on it, but I guess that's for V2.0
Not many build pictures...
But I was building this when I was in the closing stage of my house, and my welder and table was still at my parents house (No way I was taking it with me to my apartment!)
My dad saw me building one, and figured he'd lend a hand and make up some sides for it!
It's all scrap hardwood from pallets he gathered at his work.