I love the idea of a covered round pen with lights for evening use. I also really like the higher walls for the more. This one really catches my eye because it doesn't seem as claustrophobic as the other high-walled round pens.
For the horseman on a budget, this run-in-shed-turned-stall is an excellent option. An attached tack room or grain storage area keep everything close at hand in an area that neednt be more than about for one horse.