Measure the distance between your gate posts and subtract 1/2 inch of clearance space for the gate latch plus enough clearance space for the hinge you intend to install, using the measuring tape. Make note of the final measurement.
Measure the distance from the top of your gate posts to the highest point on the ground. Subtract 2 inches from that figure for clearance when opening and closing the gate. Make note of the final measurement.
Using the power saw, cut enough pickets to cover the gate frame's width, with their length equal to the measurement obtained in Step 2.
Measure and mark two 2-by-4 boards equal to the width measurement obtained in Step 1, using the tape measure and pencil. Draw a straight line across the boards through the pencil marks, using the carpenter's square.
Cut the boards along the pencil marks; they will function as the horizontal support rails for your gate.
Lay the rails flat on a level surface, using the tape measure to space them evenly so that they will be at the same levels as the fence rails.
Position a picket at each end of the rails, aligning their outside edges with the outside edges of the rails. Align the tops of the pickets so that they will be level with those of the fence.
Drill two staggered holes through the pickets at each point where they overlap the rails, using the power drill and drill bit.
Insert a 1 1/4-inch wood screw into each hole and tighten them firmly into the rails, using the power drill and Phillips screwdriver bit. Maintain a 90-degree angle at each inner corner formed by pickets and rails, using a carpenter's square.
Turn the gate over, picket-side down.
Position a 2-by-4 board diagonally across the frame, with its top end on the side where the latch will be located and its bottom end on the side where the hinges will be located.
Mark the 2-by-4 where it needs to be cut to fit between the top and bottom rails, using a pencil and carpenter's square. The angle will be approximately 45 degrees.
Cut the bracing board along the pencil marks, using the power saw. Insert it into the frame.
Drill two holes through the top side of the brace, 2 inches in from the cut end of its bottom edge, using the power drill and bit.
Drill two holes through the underside of the brace 2 inches in from the cut end of its top edge.
Insert a 4-inch wood screw into each hole and secure the brace firmly to the rails, using the power drill and screwdriver bit.
Position additional pickets on top of the frame between the end pickets and drill two staggered holes through each one where it meets the top and bottom rails.
Butt the pickets against each other or use a scrap of wood to make uniform spaces between them for a more open appearance.
Insert a 1 1/4-inch wood screw into each hole and attach the pickets, using the power drill and screwdriver bit.