Owning horses cost money and little funds exist for luxuries like a round pen for riding and training. The stereotypical image of a ground pen costs more money than an average horse owner can afford on a budget. That does not mean it's impossible to build one. With a little persistence and alternate materials, you can build a serviceable round pen that you can upgrade with better materials as your budget permits.
Choose a location for your round pen with a diameter of at least 40 feet. Round pens smaller than 40 feet do not have enough room for riding or lungeing. Clear rocks, grass, trees and plants from a circle one foot wider than the desired pen.
Soften the soil with a tiller to create suitable footing.
Plan the location of your posts using a piece of string the to determine the radius of the round pen. Fasten one end to the ground at the centre of the pen. Use the other end to measure the distance from the centre of the pen to the posts. Then use a regular measuring tape to measure between posts. Start with the gate posts, leaving a 6-to 8-foot space between them for the gate.
Use a post hole digger to create the holes. Make the holes about a foot deep for posts. Plan on using wood posts on either side of the gate. If you can afford it,use wood posts for the remainder of the posts for the best round pen possible. You can also use inexpensive green metal landscape posts.
Install the railing material on the outside of the pen. Wrap electric tape (between 2 two and four inches wide) around the perimeter of pen, sliding the tape into the tabs on the posts. Repeat two more times at different heights. You can nail the cheap electric tape to wood posts, too.
Other materials include vinyl railing, which comes in rolls, and wood, which may be expensive. Thinner wood such as 2 by 2-inch pieces reduces the price.
Install the gate by purchasing a metal gate and following manufacturer instructions, or create a wood gate out of five pieces of wood, two hinges and a rope. Four pieces form a rectangle with the fifth piece crossing over the centre. Nail each piece together. Attach hinges on one side and screw onto the post. Create a latch by forming a loop on one of the rope and knotting the other to the gate on the opposite side of the hinges. The loop circles the post. Just lift off to enter or exit.
Upgrade your materials as money allows.