Spray paint the perimeter of the shed on the ground. Dig a channel on the painted line, 24 inches wide and 12 inches deep. The walls and bottom of the footer should be straight and flat, respectively.
Place a rebar chair every four feet along the bottom of the channel. Lay two pieces of #5 rebar across the chairs around the entire footer. Bend the rebar to fit around corners with a rebar bender. Tie the rebar to the chairs with rebar ties.
Measure the area of your footer and order the appropriate amount of S2 concrete. One yard (27 cubic feet) of concrete will cover about 20 feet of footer. Order a calcium additive if you plan to pour during winter in a cold region.
Pour the concrete and smooth the surface with a concrete float. Allow at least 24 hours for the concrete to cure before building a shed on it.