I'm envious; I want a root cellar. But I'm a West Coast girl, and the West Coast, in general, doesn't know about celllars or basements. I'm not sure, but I seem to remember reading once that a dirt floor covered with gravel is recommended for root cellars. The dirt floor helps keep the humidity up (? I think ?), and the gravel keeps things up off the dirt. I could be wrong about this, but you might want to check it out before you pour the concrete . If you build this I hope you will take lots of pictures, and keep us updated.