That link is similar to what I am going to make. I've already got a 125g as a filter/sump waiting to be drilled and setup. Once that is done I am going to start on the frame, it will not be enough for the life of the fish but it will be large enough to keep him happy for a long time. I am thinking 6.5' x 4.5' x 3' due to where I am putting it at this time, I could adjust it slightly but that is pretty big for the small area I am working with. That pond plus the water in the sump/filter would easily surpass 600g. That is my plan, it may change slightly but more or less that is what I am working with. I thought I could go bigger but I finally measured the area and it is smaller than I thought. That size should hold the cat over a few years at least though.