If you're talking about for a round bale, I saw one the other day in a neighbor's pasture and went "duh", lol! It was very simple but you could add to it to make it whatever you want. Somebody had taken 4 probably 10' -12' treated 4X4s, and sank them in the ground so that a bale would roll in one end and be locked in. There were 2X4s around the top to stabilize it (so this is taller than the horse) and 2X6s about chest high on a mid size horse, all the way around, and at ground level. That was it. The end the bale would go in was a bar arrangement that could be taken off to roll in the new bale and lock it in with one of the chest-high 2X6s. Very simple and there appeared to be very little mess.
I am not one of those who in expressing opinions confines themselves to facts. - Mark Twain
The fact that man knows right from wrong proves his intellectual superiority to other creatures; but the fact that he can do wrong proves his moral inferiority to any creature that cannot. - Mark Twain