600 gal for 2200? buy it buy it buy it.
Yeah, 2 full sheets of acrylic will cost you less, but you'll use a hella lot more cement that you might think, plus bracing, tools, fixtures to assemble it, and so on. That 600 tank for sale is proven to hold water in the long term. 600 gallons would be a LOT to have on your floor. I built a 50gal sump with acrylic and had a seam split - that was bad enough - and I'm not exactly a duffer when it comes to building stuff. 2200 for a proven, assembled tank is a STEAL.