Lay the lumber on the ground and measure and mark four sections that are 36 inches long. These are the sawhorse's legs.
Measure and mark one section of lumber that is 48 inches long. Cut the lumber on the marked lines with a miter saw.
Push two of the leg sections into the bottom of the metal saw horse brackets. Fasten the wood to the bracket with four 1-inch screws through the bracket and into the wood. Repeat this process to build the other leg.
Open the top of the bracket by pushing the legs together. Insert the 48-inch lumber into the top of the bracket and open the legs to lock it in place. Repeat this step to fasten the legs to the other side of the cross member.