Building a shed door is a relatively basic project. A shed door, for stability, is built out of a box shape using 1-inch-by-4-inch wood beams or 2-inch-by-4-inch wood beams and a 1/4-inch sheet of plywood. A more durable and heavier door uses the 2-inch beams. The most important aspect to the project, as it is with many projects, is to carefully measure the opening. A slight deviation of 1/4 inch could cause the door to rub against the frame, wearing out both structures.
Measure the height and width of the opening for the door carefully. Transfer the measurements to a sheet of plywood and mark the dimensions with a pencil. Cut the sheet along the marks with a circular saw.
Hold the cut sheet of plywood in place over the opening to verify the measurements. Mark any adjustments needed onto the wood and cut with a circular saw.
Cut two 1-inch-by-4-inch planks to the width of the door with a miter saw. Hold the planks against the cut plywood to verify the size. The ends of the plank should be flush with each edge of the plywood sheet.
Spread wood glue along the face of each plank and press the glued face against the plywood so that one plank is flush with each side of the plywood and the top of the plywood, while the other plank is flush with the bottom and sides. Clamp the planks to the plywood.
Drive 1-inch screws spaced every 8 inches with a drill and screwdriver drill bit through the face of the plywood into the sides of the planks.
Repeat the process with two additional planks that will stand vertically flush with the edges and pressed against the edges of the upper and lower horizontal planks. Cut the vertical planks to the height measurement minus eight inches. Attach the planks to the plywood with glue and screws.
Measure the distance from the inside edge of one vertical plank to the inside edge of the second. Cut a fifth plank to that measurement. Install the plank centered between the top and bottom of the door and pressed against the inside edges of the vertical planks with glue and screws.
Attach straight brackets, which are simple metal strips with screw holes, over each joint between wood planks with 1-inch screws for added stability.