Mark an outline for an 8-by-10-foot shed with stakes and builder's twine, in a flat area with good drainage. Face the opening away from any prevailing wind. Square the outline by measuring with a tape measure between the corners and adjusting the stakes until the diagonals are equal. Rake the area clear of leaves or debris.
Set nine 4-inch solid concrete blocks for a foundation, one in each corner, one in the middle of each wall and one in the center of the shed. Lay a long board across the tops with a 4-foot level on it and adjust the dirt under the blocks until the tops are level in all directions.
Frame a floor with 2-by-4-inch pressure-treated lumber, two sides 10 feet long and two ends 7 feet 9 inches. Nail the side bands into the ends with two 16d framing nails driven with a hammer into each board. Cut 4 boards 7 feet 9 inches with a circular saw and nail them 24 inches apart between the ends for floor joists. Cover the frame with 3/4-inch plywood, fastened to the bands and joists with 8d galvanized nails. Use two full 4-by-8-foot sheets and one cut in half lengthwise.
Put the floor on the foundation blocks, aligned with the block edges. Test it with a level and make any needed adjustments. Build a back wall with top and bottom plates 10 feet long and two side walls with plates 7 feet 5 inches long. Nail plates into end studs to make a rectangle for each wall, square it with diagonal measurements and place interior studs with centers set 16 inches apart.
Raise those walls, brace them plumb with a level using boards nailed to studs and to stakes in the ground. Nail the corner studs together. Make a front wall with a rectangle of top and bottom plates 10 feet long and two studs set 16 inches in from each end and two studs together in the center of the wall.
Build two headers each with two two-by-fours side by side with a 1/2-inch strip of plywood between them. Nail one on each side between center studs and two outside. Cut 4 studs to fit between the top of the bottom plate and the bottom of the header. Nail 2 on each side to the full studs to frame the outside of the door opening. Tie the walls together with cap boards, 8 feet long on the sides to extend over the side walls and 7 feet 5 inches long on the ends. Add a full 10-foot cap on the front wall to make a roof slope.
Cover the side and back with 1/2-inch plywood panels, 4-by-8-feet, set vertically. Use two full panels on the side walls, two full panels and one cut in half lengthwise on the back; put the cut panel in the center. Fasten panels to studs with 8d nails. Cut plywood to sheath small spaces on each end of the front wall.
Install six rafters the width of the shed, using 9-foot two-by-fours. Trim the bottom of the back ends to fit flat on top of the back wall. Cut a 1-by-3 1/2-inch notch in the front end where a rafter meets the wall, so it will fit on top of the wall with an extension over the front. Nail rafters to the walls 24 inches apart with two framing nails on one side of each rafter and one on the other.
Roof the shed with corrugated vinyl panels; panels typically are about 26 inches wide, designed to cover 24 inches of roof, so five panels 9 feet long should cover the roof. Overlap panels by one ridge and one valley where they connect. Fasten these to the rafters with a screw gun and galvanized screws that have a plastic washer cap.
Make two doors of plywood to fit the front door frame. Measure that space and divide it in two to figure the width for each door. Build door frames of two-by-fours with 4-inch faces up. Miter the corners at 45 degrees to make a rectangle. Put a 2-by-4 horizontal brace in the horizontal center of each frame. Cut 1-by-4-inch braces to fit diagonally between the corners of each half of each door frame. Cover the frames with plywood.
Hang the doors with metal strap hinges, similar to those used on gates, screwed to the door frames and the sides of the rough door opening. Put a latch on the center studs to hold the doors when closed.
Trim the walls with 1-by-4-inch boards at the corners and over each seam of plywood. Add top trim to cover openings between the wall siding and roof. Put trim on the outside of the doors, two boards vertically on each side and one horizontally across the top.