You are right AZBill, but as Old Sarge pointed out I will be covering it with earth, somewhere around 12" or so. I got some of the bags from a company in california cwillis. Don't remember the name, just found the company with the cheapest sandbags and shipping. I only ordered 300, I have scavenged the other 400 from various sources, all new bags. My total cost will be in the neighborhood of $300 because most of the materials I have on hand. If you will look at the link that oi888 put on the first page they have a FAQ section that tells some companies they get their bags from. They actually use a larger bag than I am using which equals more stability. I am using standard sandbags, they use misprinted polyethylene or polypropylene (can't remember which) grain sacks. They have several designs and pics on that website ravingbantha for above ground structures that might give you some ideas. You have valid concerns BlackhawkFan, but on the same website you can see testing that has been done concerning burst strenth of the sandbags as well. I will put a footer on my center column which will in turn support the ends of the main beams, the walls will support the rest. Think of a ferris wheel oriented vertically. That is how the roof will work in a sense, one center column with four large beams radiating out to the walls and within those beams will be a network of dimensional lumber beams covered in sheathing.