How do I make a simple lean-to for one horse?

Question

How do I make a simple lean-to for one horse? My mare is out in the rain and i have no barn.

Answer 1

Do you have a horse trailer you could park out there temporarily? Or can you like up some round bales along the fence so she could at least get out of the wind?
The simplest way is to take some long poles and dig with a fence post digger. Then take a spade and make the hole a little bigger for thicker posts. Two of them should stick out of the ground a little further so the roof will have a slope. Keep the mare away from the holes until you get them filled back in.
Find some tin, wood or even trucking tarp (temporary fix) and attach it to the poles for sides, but the roof should be more sturdy.
This sounds pretty backwoods, I know, but you can make a more permanent structure in time.

Answer 2

If it is on the side of the buiding you can use post and beam constructions and use treated plywood for a roof,
You could also use tin for the roof
Still take some work to do it correctly.
I would suggest get a prefab movable stall or pipe stall.

Picture of the most simplest plan I can see.
http://www.quickstalls.com/pasture.htm
This should give you an idea how simple one can be.