When erecting a new outbuilding, shed or house, one important element is the exterior covering. If you leave the plywood walls exposed to the weather, they will quickly warp and rot. Aside from its protective qualities, the exterior sheathing makes the first impression on all guests and passers-by. Although you can use many types of exterior siding, including vinyl-covered aluminum siding, faux bricks and stone, you may prefer to use shiplap siding, where boards are shaved or routed on opposite sides so that they interlock.
Lay a course of shiplap across the bottom of the building exterior. Use a level to check that you lay the courses evenly. If you have a helper to hold the far side of the board, this will make it possible to use longer boards. If the exterior is longer than the shiplap boards, stagger the seams.
Place one nail every 6 inches, 1 inch above the routed channel for 6-inch-wide boards. Insert the galvanized nail perpendicular to the board's surface. For boards 8 or more inches wide, place two nails, one above the other, every 6 inches.
Fit the second course above the first course of shiplap, leaving a 1/8-inch space between the edge of the top board and the edge of the cut-in where the shiplap was routed out. This will allow for 3/8-inch overlap on a 1/2-inch shiplap. Check that you lay each course level and continue nailing as described previously. If necessary, compromise between spacing and level, but always make sure that there is sufficient overlap to keep the rain out.