Dig out an area under the supports for the shed by at least 3 inches using a shovel and a wheelbarrow. Tamp the soil using a pole tamper to create a hard surface. Fill in the void with gravel and tamp again. Set your shed on top of the gravel footings to keep the bottom of your shed dry, even during rainy seasons.
Dig out a French drain around the perimeter or uphill side of a shed if extra water tends to flow towards the shed during rainstorms. First, use a shovel to remove at least 8 inches of soil in a trench about 8 to 12 inches wide. The wider the trench, the more area is available for drainage. Position the trench to reach the drip line of the shed if digging around the perimeter. The drain will catch the roof runoff and keep it from puddling under the shed.
Check the grade of the drain with a level to make sure that the bed of the drain slopes away from the shed. Typically, this translates to 1 inch for every 10 feet of horizontal run.
Line the bed of the trench with landscaping fabric to prevent the soil from filtering in and clogging the water carrying capabilities of the drain. Leave enough draped over the sides to wrap back over the top of the trench later.
Lay 2 inches of gravel in the bottom of the trench, smoothing the stones even with a garden rake.
Place a 4-inch perforated PVC pipe at the center of the trench, on top of the bottom layer of gravel. Lay the pipe with the holes on the top. Check with a level to make sure you still have the pipes moving the water away from the shed.
Fill in all but 2 inches of the drain with more gravel. Drape the sides of the landscaping mat over the stones so that the cloth overlaps in the center. Fill over the cloth with 2 inches of gravel so that the drain is level with the surrounding surface.