Late to the party but I have been using hay huts for probably the past 10 years. There are 6-7 horses in each pasture and after a couple of rounds of musical windows everyone settles down since there are 8 windows. Good for round bales or throwing flakes or setting bales inside. My guys eat the hay down to the ground.
It’s made of 2 sides and the halves could be individually fastened to the side of a building to contain the hay.