My adavce would be make it as big a you can to fit in your stand or where ever your going to put it. My 1st one I made out of a 20gal long and hated it after awhile as I started to run out room as I upgraded things. From my experience you realy can't go to big when comes to the size of it. But as others have said pick out a skimmer and then built your sump around it. I still wish I had more in mine so i could have area for frags one just for the heaters, one for a fuge, and one for reactor pumps and what not, I feel it always nice to the room to expand.

