Other than just the space that my basement fishroom provides, what I'm really happy with is the utility sink.
Like Naesco suggests, consider the tank on the main floor with basement sump. For a center build like this
walk around (plus lots of other nice displays in the Waterpix forum). Still can do a in-wall upstairs against a closet for access or backing into another room (
Dez's) and still have basement sump. What I did was a room divider type (picture in my signature).