Housing horses does not always have to be expensive. While it is true that keeping horses is far more expensive than simply buying them, that does not mean you have to spend a fortune on their shelter. Horses survived for many years without the protection that humans have given them. A simple protection from wind, rain, sun, and the elements is all that a horse needs for shelter.
Measure your shelter and mark the corners with your stakes. A simple shelter can be 12 feet wide, 12 feet long and 10 feet high.
Dig holes for your 4x4 posts. These need to be at least 36 inches deep. Set the corner posts in cement. They will need to set for 72 hours before you do anything else.
Attach your plywood to your corner posts, leaving one side of your shelter open. Nail these in securely and make sure the plywood pieces are at least six inches from the ground, so they will not sit in the wet when it rains.
Nail a 2x4 lumber piece to the tops of the 4x4 posts at the front and back of your shelter. This will form the basic frame for your roof.
Apply the siding to the 2x4s by nailing them securely at each end. Place each section of siding slightly overlapping the other, and attach the siding pieces to each other with roofing nails. When complete, you should have a three sided shelter with a metal roof that will shed water.
Choose a dry place to build your shelter. Don't put it in a flood zone.
Be sure to use caution when handling siding. It can be razor sharp.