Saw 1-by-6-inch lumber into pieces tall enough to fit your doorframe. If you have not constructed a doorframe yet, decide on your total height and width and cut boards to fit those figures. These boards are the battens that will form the door itself. Lay the battens side by side to ensure that you have enough for your door width.
Cut down 2-by-6-inch lumber to form three ledges measuring the width of the door, minus approximately 2 inches on either side. For instance, a 3-foot wide door would have ledges that measure 2 feet, 8 inches. For braces, cut 2-by-6-inch lumber diagonally so that when placed against the door it will measure the approximate width of the ledges. Determine the space between the ledges, subject to the height of the door, and cut the braces to be that long when placed diagonally.
Saw the top and bottom of each brace to lay flat against the tops and bottoms of the ledges.
Apply a commercial wood preservative with a paintbrush to protect the door from possible weather damage.
Attach the first batten to the three ledges, 2 inches from the edge of the batten. Screw each ledge into place using three 2-inch screws.
Fix the rest of the battens to the ledges, pushing them as close to one another as possible, and screw each into place with 2-inch screws. There should be two uncovered inches of wood at the end of the last batten.
Lay the braces diagonally against the door, so that the tops and bottoms of each align with the braces it intersects. Fix the braces into each ledge using 4-inch screws placed 1 inch from the edge of the brace. Follow through with three 2-inch screws, placed through the each brace and into at least every other batten. The finished door with the braces visible should resemble two “Z's” placed on top of one another.
Screw three shed door hinges into the door, spaced evenly apart, ready to be fixed into the shed.