Things You'll Need
Two 4-by-4-inch pressure-treated posts (length calculated in step 3)
4-by-4-inch nonpressure treated posts (length and number calculated in step 3)
6-foot long 2-by-6-inch boards
Two 2-by-6-inch boards that are 1-foot less than the height of the pen
Four heavy-duty hinges
4-inch wood screws
Round pens are used to hold horses, cattle, llamas and other livestock. They are places where you can train and work livestock in a confined area. It is important that they are built sturdy enough to be safe for the type of animal they will be used for. Modern round pens can be bought as prefabricated metal panels that lock together, but these are expensive. If you are willing to invest your time and labor, building your own round pen is a cheaper option.
Determine the size of round pen you want; for horses a 60-foot diameter works well while smaller animals need a smaller size. Work out what height you will need; for cattle and wild horses 6 feet or more will be required while for quiet horses 4 to 5 feet will be high enough.
Choose a flat location that is not prone to waterlogging and mark out the boundaries of your pen. Drive a stake into the ground at the center and attach a string half the size of the diameter and use that to guide you as you mark your circle. Pick up any loose stones or rocks from the area.
Multiply the diameter of the round pen by 3.142 to get the circumference, or distance around the edge. Subtract 8 feet for the width of the entry gate then divide the remainder by 6. Take that up to the nearest full number and this is the number of posts you will need for the round pen. Work out the height of the posts you need to use by allowing at least one-third of the post to be in the ground. If your round pen is going to be 5 feet high, you will need 8-foot posts.
Decide on the location of your entry gate and dig a hole on either side spaced 8 feet apart. Place a 4-by-4 pressure-treated post in each hole, backfill with concrete and allow it to set. Dig the other holes 6 feet apart all the way around the circumference. Place the 4-by-4 nonpressure treated posts in these holes and backfill with soil or concrete depending on your local soil consistency.
Screw the 6-foot boards around the pen. Begin 18 inches above the ground unless the pen is for small animals, then start lower. Have the gaps between them no more than a foot apart until you reach the top of the posts.
Construct your entry gate using the two boards that are a foot shorter than the height of the pen. Lay them on the ground and screw 6-foot boards at the top and bottom and across the width with gaps of no more than 1 foot between them to make a basic entry gate. Use cinder blocks to prop it up a foot above the ground and screw it to one of the pressure-treated gate posts using the heavy-duty hinges equally spaced along the length.
Tie two loops of rope on the side of the gate that swings open and put two screws on the outside of the gate post with about 2 inches protruding that you can loop the ropes over to keep the gate closed. Make sure you place it outside the round pen so that an animal left inside cannot hurt itself on the protruding screws.
Pressure treated posts last longer but nonpressure treated posts are cheaper. Your budget will determine what you use. Second-hand lumber is suitable to build round pens with and can save costs.
Picturenet/Blend Images/Getty Images