A lean-to is a simple three-sided structure with a sloping roof. Often the front -- the largest side -- faces away from the prevailing wind and weather, and the roof reaches completely to the ground. A lean-to's other two sides are triangular in shape; some builders enclose these sides, but the sides may be left open. A lean-to with a 2.4 by 3 m (8 foot by 10 foot) roof can be constructed in a day's worth of work. One full cord of wood stores under its roof.
Bury the ends of two 10 x 10 cm (4 x 4 inch) posts 2.4 m (8 feet) apart -- outside to outside. These posts serve as the vertical uprights of the lean-to. Bury the posts deep enough so the bottoms are equal or below your area's frost depth. Above ground, they should be 1.8 m (6 feet) tall. Plumb the posts so they are perfectly vertical.
Build an 2.4 by 3 m (8 foot by 10 foot) rectangular box using 5 x 15 cm (2 x 6 inch) timber. This becomes the frame for the roof. Fill in the roof frame with 5 by 15 cm (2 x 6 inch) joists, 40 cm (16 inch) on centre away from each other.
Cover the roof with 1.8 cm (3/4 inch) plywood. Install steel roofing or shingles over the plywood.
Nail a 5 x 25 cm (2 x 10 inch) header board to the front of the two buried 10 x 10 cm (4 x 4 inch) posts. Make the header flush with the outside and top edges of each post.
Set the roof onto the header. The roof hangs over the front of the header by one foot and slopes to the ground. Make note of the position it touches the ground.
Bury two 10 x 10 cm (4 x 4 inch) posts at the point where the roof touches the ground. These posts should rise 30 or 60 cm (1 or 2 feet) out of the ground. Add a header to these posts.
Nail the roof to the front and rear header boards. The basic structure is finished.
Finish the triangular sides of the lean-to with 2.5 x 15 cm (1 x 6 inch) cedar boards. Leave a 7.5 cm (3 inch) gap between each board. Run the boards from the front post to the outside edge of the roof.
Scale the lean-to up or down based on your needs.