Build first a concrete slab frame, then remove the frame, but keep the stakes in place and dig at least 4 inches down. Add the gravel and use a hand tamper to compact it. Repeat the procedure until you have a 4-inches gravel bed. The concrete should be mixed according to the packaged instructions. Set the frame in its original location. Then on top of the gravel, pour the mix concrete into the frame. Draw a straight -inch-by-inch board across the concrete to screen the surface. The concrete will be graded and smoothed out using the screening technique. Smooth the concrete with a concrete float once it has lost its gloss. Create a nonslip surface by using a stiff broom, Finish the edges with concrete edger, then spray the pad with a concrete cure and seal product with a garden sprayer. Remove the frame when the concrete has cured.