Pretty much as in the homesteadeconomics video, cold rolled sheet steel, what he called masonery sand but is what I later discovered is paver sand (I used the coarsest sand I could find, which was totally wrong but it seems to have worked well enough and in all honesty, as I just laid this on the ground, it worked out better for me as it minimised any leakage, although the ants seemed to love it, I can always top it up with paver sand if I get any settling, but after nearly two years it has stood up well. The stones were left over gabion stones (I am working on a gabion fence - long story but I will get there one day).
As this is only ordinary steel, it obviously won't last forever, but it will outlast me I am pretty sure.
The only thing I would do again is to try and invent some kind of forming system to curve the steel sheet as it was very difficult to keep perfectly circular, and I am a bit OCD about those kind of things.
It's a brilliant, if rustic, design and I would thoroughly recommend it if you like that style.
