How much do you want to spend? A Rubbermaid Commercial Stock Tank would make a nice frag tank. On the other end of the spectrum, a custom shallow tank is also nice. Will this be a display tank or something in the basement that you just want to grow frags in? Is this to make money or just for fun? If Trying to make money, go as cheap as you can so you don't lose much if it doesn't work out. If it is for fun, make it as nice as you want.