My shed is 12x20 and the area that put the shed wasn't level. So I used rail ties and built a 16x24 pad with crush and run in the center. I used 2 ft sections of rebar and drilled holes in the ties and hammered them through to anchor them into the ground. I used a full load of crush and run, 10 rail ties, and 30 sections of rebar. Leveled the area and have had no issues for 5 years now.