Shed made from Pallets! This photo shows a "before" pic but you could make so many things using this basic idea. Now to find pallets! http://www.oklahomahistory.net/ttphotos9a/Pallets031409b.jpg
Run-in, but paint it pretty...
horse shed plans | Next Free lean to horse shed plans | trony
How to Build a Run-In Shelter for Horses, Cows, Goats, etc. for under 300.00 dollars. This would be a great temporary shelter for the big field.
Run - Ins - Horse Sheds -Designs - View Our Plans - Ga Barn company
For the horseman on a budget, this run-in-shed-turned-stall is an excellent option. An attached tack/feed room keeps everything close at hand in an area that needn't be more than about 16x12' for one horse.
Inexpensive mini horse shelters
Loafing Shed Plans Elevation
With an angled roof of course. But love the storage room on the side, awesome idea.
horse barns and stalls | horse shelter putting on finishing touches on horse shelter shop