Select the location where you want the gate constructed and dig two holes, both two feet deep and one foot square, spaced out from the desired on-center width of the gate. Dig out six inches of dirt between the two holes.
Position a 4-inch-by-4-inch post in each of the holes and fill the remaining space with concrete, making sure the posts stand upright and the space you dug between the holes is filled.
Measure the length between the insides of the two posts and allow for a space of one-half inch on either side between the gate and each post.
Position 2-by-3-inch wood pieces to form a rectangle measuring 5 feet in length and your desired width. Measure the length of the diagonal of this frame and cut a 2-by-3-inch piece of lumber accordingly, laying it diagonally across the frame from one upper corner to the opposite lower corner. Fix all pieces together using galvanized nails to form the framework for the gate.
Nail 1-by-4-inch or 1-by-6-inch fence boards, or plywood cut to this size, onto the face of the frame, spacing them evenly between the edges.
Secure three T-hinges evenly spaced apart, on the outside of the gate for an outwardly opening gate and on the inside for a gate designed to open inward, onto the gate and one of the posts using nails or screws.
Place the latch opposite the middle hinge and cut a hole into the gate directly above it to allow your hand to pass through and unlock the gate from the other side.