Our original green houses had no base frames. They are held down with 1/2 inch wide homemade wooden pegs (like tent pegs only wood) driven into the ground at the bottom of a bent cattle panel and secured with zip ties and baling twine as needed. The length of the pegs are about 10-12 inches (made from scrap wood).
This year our original greenhouse is being jacked up and placed on a base. Currently I must hunch over to work in it and I hit my head often (OUCH!) The base frame will be constructed from 4 X 4 boards that are bolted to one another using long lag bolts and then reinforced with L- brackets. We used two cattle panels overlapping each other.
We used 16’x50” galvanized cattle panels. The dimension of the greenhouse is based on the number of panels used and space available so the houses I have are different lengths and the same height (about 5ft.) We use the heavy clear rolls of plastic that is on sale when my husband shops and Tyvek tape (It is what we had when we first built and works like a charm.) It is strong and easy to use, waterproofing tape. I can fix a hole or scratch from a cat in an instant. We also tape our plastic together when we put the plastic on the house in the fall with this tape. The goal of most of our projects is that it is simple enough that I (an unskilled carpenter) can fix and repair things when my husband is unavailable. I know we could have a better greenhouse if we invested more and perhaps save some money in the long run. We often started projects when we feel a need and just build from this desire with what we have. In this case I did not want o watch my lettuce die in the frost, Knowing I could extend the growing season with some plastic covering we made the cattle panel greenhouse. Improvements are happening as the current houses become disheveled from the weather and animals through the years. I will update later as we are doing some now with the jacking up and facelift I have requested.