It would be easy to strengthen this greenhouse design with rebar. The same basic idea could be used to build low cost ferrocement housing, shop space, etc. by adding rebar, small mesh and cement plaster.
“I was able to put the greenhouse up in a week. It now has chicken wire along the bottom with nylon screen on the inside with 1/4 inch square holes in it. I closed it in with plastic for the winter and the broccoli plants are still growing from last year. One thing I found handy with this greenhouse is as the tomato plants grew taller and taller there was always a place to tie the plants up to. I added temporary supports down the middle to handle a wet heavy snow (2×4 posts with a short 3 ft piece screwed to the top).”