I was going to provide links to a couple of interesting charts...but then realized that you were no longer talking about bulletproofness to various categories of small arms fire, but rather about construction. Never mind.
I've never built a tank taller than 24 inches, so can't comment. I will say that if I were doing this, I would be looking really hard at concrete. Wiring together a rebar reinforcing structure is child's play; and I literally just this week finished working for the first time with the no-mixing concrete product; just dump it into the form, pour in the water, and stand back. Hardens in a half hour; I think full cure is something like a week. It costs almost 50% more than regular concrete, but IMHO it is well worth the cost. My project was a couple of heavy timber gateposts (10-inch timbers, in 24-inch-diameter holes 5 feet deep), and a half-dozen smaller fenceposts (4-inch diameter, 14-inch diameter holes, 3 feet deep) so not directly related to aquarium use. Once the holes were created, setting the posts and doing the concrete work took about 10% as much time as I would have spent mixing old-fashioned concrete. I'd look into it a lot further before moving forward in that direction...but I gotta admit that the entire time I was out there sweating and swearing, I had visions of a big-ass outdoor tank clouding my mind and warping my judgment.
Good luck with whichever path you choose, and keep us updated!
