I actually built one of these a year ago, out of a shopping cart I didn't know what to do with. I'd never seen this one, but my design is almost the same. This one is shininer though. Frankly, mine is incredibly uncomfortable to sit in and I never used it. The front is also quite fragile, as it was not built to hold that much weight, and all the support structure for the front half is cut away. If you're ever in a shopping cart race with some other folks though, this is a sure way to win the aesthetics prize.

If you want to make your own, it's not very hard. All you need is a dremel with cutoff wheels or an angle grinder. And the determination to have a very silly chair.