Because of the sloping terrain and city codes regarding minimum foundation thicknesses, it ended up taking 96 80lbs bags
96 80lb bags would only cover 115 square feet at 6". And if it's a slope, it would have to be smaller than 10x10. Where do you live where they have building requirements for such a small shed? In AZ, you don't have to care at all until you go over 200 square feet.