If you want to keep a horse on your property, you'll need to house it in a proper stable. Horses aren't like automobiles. They require specific care, and the stable you build needs to be as much of a home for them as your own house is for you. Generally speaking, you should only undertake a project like this with the aid of professional builders. If you have the skills and the resources, however, you can build a horse stable to match the specifications of your property.
Determine the size you will need for your horse stable. Your average horse requires a stall of about 12 feet by 12 feet for adequate comfort. You will also need to factor in room for hay storage (each horse consumes 2 to 4 tons of hay per year) and a feeding stall as well. In addition, you may need to include space for equipment storage, a wash rack and/or grooming area, locations for doors and windows and amenities for water and electricity. A horse will need a running paddock as well as a stable, so make sure you include space for that on your property as well.
Select the type of building materials you will use. Building wood is typical for most barns, but you may wish to use a stone or steel framework to help provide stability. Pressure-treated lumber is fairly strong and will last a long time, but beware of cedar: it contains oils that horses like to chew on!
Decide what kind of electricity needs your horse stable will have. Wiring should be sheathed in proper metal conduits (mice will chew at it otherwise) and meet all local safety standards. This is especially important in a stable, where hay and other combustible materials can easily start a fire.
Determine the right water needs for your stable. Not only will water be used for your horses to drink, but it is an absolute necessity when cleaning the stable out. In addition to proper water storage and flow, be sure to keep drainages in mind, so that you can wash waste products out of the stable safely and cleanly.
Choose a good roof for the horse stable. Metal roofs make attractive options because they are easy to install and last a long time. The specifics, however, depend on aesthetics and your particular needs. Be sure to include proper ventilation in your roof and insulate it against the weather if necessary.
Notify your local government of your plans to build and be sure to file all forms correctly. A building inspector will likely need to approve of your structure before you can legally build it.
Adhere to any and all safety measures you can conceive of. Horses can find a remarkable number of ways to injure themselves, and the safer you can make their environment the better. This includes things like protruding nails, unsteady planks and sharp edges on doors and walls.
Make sure your horse stable has proper ventilation. Dust, smells and bacteria from droppings can stagnate and cause significant health problems. Well-circulated air with decent ventilation will go a long way towards curtailing such issues and ensuring a healthy animal.