I am not sure if this was responded to, but it is best to locate an engineer local to your area. The engineer will confirm that the structure will meet current local design criteria such as wind conditions, soil bearing pressure and other considerations. Because the structure is light, it may have the tendency to blow over in high wind conditions. It should be designed with concrete footings. The size and depth of he footings is dependent on the soil conditions, the size of the structure, and the wind loads expected for your area. The The local building department or engineer should be able to provide you with the information you require. Do not be surprised if the engineer charges a fee for his services. Good luck with the project!