My tank will be around 400 gallons. I'm planning on making it very similar to
Gary's solar shed tank which is also around 500 gallons. This is similar to the $1000 solar project one, just larger.
I do have a few changes I'll be making to the design and I haven't worked them all out quite yet. The tank is the next thing on my list to start working on. But, I know I will be using a different liner than he is. He used EPDM pond liners for his tanks and I am looking into using a paintable liner. The cost is less (~$100 vs $160) and thats the main reason I'm opting for it. It is also probably a bit easier to put in since the pond liner has to be folded. The other thing I'm thinking of doing is insulating more than most of have done before. I think his tank is insulated to around R30. I'm planning on insulating mine to at least R40. My insulation will also cost less because I'll be doing it mostly with cellulose (sealed from water of course) versus foam board.