I'm fencing in another pasture at home and need an idea for a cheap, temporary run-in shed. I am building a permanent run-in shed, but until then would like something temporary my horses can stand under when it storms.
Or, you can go with a metal carport type structure. That's what we used for our horses. We put trim around it and had the legs made 1' taller so they wouldn't bonk their heads. Delivered and installed our 18x21' shelter was around $700. I've attached a picture of ours. We put tarps up on one side during the winter. For summer storms it was fine the way it was.
No offense, but I'd be very careful about shelters like that. I've seen similar looking ones, and they didn't look sturdy enough to be used in a horse field. Depends on horses I'd say (wouldn't work for mine as they run, kick and smash against the walls all the time)!