Thanks, Evan.

I have been looking into this more and think it would be better (and probably cheaper) to build one from scratch rather than try and adapt my aquarium lights. I'll need more ballasts anyway. So I am looking at getting 6 or 8 18" T8 tubes (F1ST8-BL) and 3 or 4 double ballasts.

Does this sound OK for doing up to 11 x 14? What is the advantage if any of using (more) T5 tubes?