Typical sheds are not complicated. They are simple buildings used to store tools or other items, and they have no need for insulation or a fancy appearance. Some metal sheds use a sliding door, but this type of door almost always binds or bends because of a metal track that wears out, and you end up removing it. Most storage shed doors that withstand the test of time are built with some type of lumber or plywood. It's basic, but fits the bill with a sturdy door that may outlast your shed.
Measure the door opening. Subtract 1 inch from the height and width. Use a table saw to cut a piece of CDX plywood -- which is exterior-grade waterproof plywood -- to the measurement.
Cut two pieces of 3/4-by-4-inch-wide poplar for the vertical sides, and two pieces to fit between them for the top and bottom horizontal pieces. Use a miter saw to cut them to length.
Add water to the powdered resin glue according to manufacturer's directions printed on the packaging. Brush the waterproof glue onto the back of all four pieces of poplar. Lay the pieces out flat to form a frame. Place the plywood on top of the frame and square all the edges.
Screw the plywood to the frame from the back using 1 1/2-inch screws and a drill/driver. Allow the glue to dry overnight.
Fasten the door to the sides of the shed using gate-style hinges. Attach the hinges to the appropriate side of the door using 1 1/2-inch screws. Attach one-half of a lockable latch centered opposite the hinges using 1-inch screws. Place 1/2-inch spacers on the bottom and sides of the door opening. Place the door in the opening and secure the hinges to the shed with screws. Remove the spacers. Flip the latch over the side of the shed. Position and screw the other half of the locking latch to the shed using 1-inch screws.
Ledged and Braced
Measure the width and height of the door opening. Subtract 1 inch from both measurements. Using the measurements, use a miter saw to cut 3/4-by-6-inch fir lumber to length, and place them side by side so that their accumulated width equals or exceeds the width of the measurement. If the accumulated width is too wide, use a table saw to trim one or more of the boards down so that the door fits the measurement.
Measure and cut one piece of 3/4-inch fir to fit flush along the top, and one to fit flush along the bottom. Screw the two boards perpendicular across the door, flush to the top and bottom using 1 1/2-inch screws and a drill/driver. Place at least two screws through the horizontal board into each vertical board.
Measure diagonally from corner to corner. Use a miter saw to cut an additional piece of fir to the measurement. Place it on top of the two horizontal pieces, spanning diagonally from corner to corner. Insert a pencil between diagonal board and the horizontal boards on each corner, and trace a line on the underside of the diagonal board to indicate the angle.
Transfer the angle to the blade of a miter saw. Cut the angles on both ends of the board using the miter saw. Place it diagonally between the top and bottom horizontal board. Screw the diagonal board to the vertical boards using at least two 1 1/2-inch screws for each vertical board.
Screw gate hinges on the door using 1-inch screws and a drill/driver. Mount the door in the opening by screwing the gate hinges to the door opening. Install a locking latch.