Determine the desired dimensions for your garden shed. To make your job easier, use a square measurement like 4-by-4 feet. Drive four stakes into the ground to mark the placement of the four corners of your shed.
Dig a square 6-inch-deep hole at each of the four corners and in between the corners to install supports for the walls.
Pour 4 inches of crushed limestone into each hole and compact it with a hand tamper. Use a level to make sure the rock is even. Cover each of the eight holes with landscape fabric then center a concrete block in each hole. Cover the fabric with another 2 inches of crushed limestone.
Cut eight equal-length pieces of 2-by-6 inch pressure-treated sill lumber to frame the shed floor. Lay one piece of lumber flat between each pair of corner blocks to create a square frame. The edges of the lumber should be flush with each other.
Set a piece of 2-by-6-inch lumber upright on each flat piece, aligning the outside edges. Attach the upright pieces of lumber to the flat pieces with galvanized wood nails and secure the corners by driving two more nails through each joint.
Cut additional pieces of 2-by-6-inch pressure-treated sill lumber and slide them inside the square frame at 6-inch intervals to form the floor joists. The edges of each floor joist should be flush with the inside edge of the floor frame. Secure the joists in place with two galvanized wood nails through each end.
Cover the floor joists with sheets of 3/4-inch plywood. To make installation easier you can purchase sheets of 3/4-inch tongue-and-groove plywood flooring and, after nailing one sheet down, slide the tongue edge of the next piece into the groove of the first. Secure the plywood flooring to the floor joists with galvanized wood nails.
Cut eight pieces of pressure-treated 2-by-6 lumber to the width of the shed and eight more to the desired height. Lay out two shorter pieces of lumber parallel to each other and connect them with two of the longer pieces positioned perpendicularly. Secure all four corners with galvanized wood nails. Repeat this process three times to complete four wall frames.
Cut additional pieces of 2-by-6-inch sill lumber to the measurement between the inside edges of the top and bottom of each wall frame. Install pieces of 2-by-6-inch lumber at 6-inch intervals along the interior of each wall frame except one. These vertical boards will serve as wall studs.
Build a door header in the fourth wall frame by sandwiching two pieces of 2-by-6-inch lumber cut to the width of the door opening plus three inches around a 1/2-inch plywood spacer. Cut two pieces of 2-by-6-inch lumber to the height of the door opening and secure each one to a full-length stud. Install the vertical studs on the wall frame then lay the door header between the top edges of the studs and secure it in place with galvanized wood nails.
Install sheets of vertical plywood siding on the outside of all four wall frames. Nail the siding to each of the studs, positioning it so that the top edge is flush with the top of the wall frame. Cut smaller pieces of siding to accommodate for the door opening on the corresponding wall frame.
Raise the wall frames so that the outside edge of each frame lies flush with the edge of the floor frame. Secure the frames in place from the inside, nailing the bottom boards to the floor joists then secure the corner joints with additional nails.
Frame the roof by cutting two pieces of 2-by-6-inch lumber to the width of the shed and two to the desired height of the roof. Attach the height pieces to the center of the width pieces, positioning them vertically to form a T shape and nail them in place. Measure the length between the top of the vertical board and one end of the horizontal board. Cut four pieces of 2-by-6-inch lumber to this length.
Lay the T-shaped frames flat on the ground and set the additional lengths of 2-by-6-inch lumber at an angle between the top edge of the vertical board and each end of the horizontal board. Cut the ends of the angled boards so the edges sit flush with the edges of the T-shaped frame and nail them in place.
Repeat steps 13 and 14 to build several more roofing frames. The first two will be used on the outside edges of the roof and you will need enough additional frames to position them at 12-inch intervals in between.
Set the bottom of one roofing frame along the top edge of one of the wall frames and nail it in place. Install another roofing frame along the top edge of the wall frame opposite the first. Lay the remaining roofing frames across the space between the wall frames perpendicular to those on which the two roofing frames are mounted and nail them in place at 12-inch intervals.
Cover the roof of the shed with sheets of 1/2-inch plywood, securing it to the angled sides of the roofing frames with galvanized roofing nails. Install asphalt or cedar shingles over the plywood sheets. Nail down the first row of shingles along the bottom of the roof so that they hang over the edge by 1/4 inch. Install the next row of shingles, overlapping the top edge of the first row by 1/2 inch. Continue installing new rows until the entire roof is covered.
Install the shed door by following the manufacturer's instructions for the particular model you have chosen. Test the door to make sure it opens and shuts smoothly.