Crossfit boxes are excellent fitness equipment if you are aiming to improve your jumps. You can make your own using 3/4 inch plywood or a similar material. One 4×8 feet sheet is enough to complete the project with plenty to spare. Screws, sand paper, and stain should be on standby as well. You will be using a drill, a saw, and clamps if you are working alone.
Design your box with focus on the dimensions. Make each of them different so that you can progress from the lowest to the highest as your leg strength improves. For example, you could make a 20x24x30 inch box. Mark each side on the plywood sheet. Cut the six faces with a saw and smoothen the edges.
Advanced woodworkers can create more secure joints to increase load capacity and longevity. Screw everything together and test its stability. If you prefer to get one readymade, then shop for one of these plyo boxes online.