I'd be interested to see a cost/benefit of doing a wood framed tank VS a concrete block tank. A poured concrete tank would surely be expensive because of all the framing labor... but if you figure anything this large will almost have to be a permanent installation, it makes sense to me to use something like concrete block that will not rot or erode with exposure. I just built a 200gal tank with plywood/glass, and I painstakingly coated every surface that could ever be exposed to water. Concrete blocks would seem much easier for a monster tank like this... although I don't know, they may come out being more expensive.