I would agree with Michael's estimation for number of tubes. I personally built something similar to the rig in Sullivan and Wesse' book: 12 20w BLB tubes, well-ventilated. Perfectly sized for a 16x20 print frame.
My own $.02 worth: build a large box. The convenience of being able to print multiple prints or test strips is worth using a 16x20 frame, and you can always put switches on ballasts to control two bulbs at a time. I print on two 10x12 sheets of paper simultaneously...a huge time and energy (thanks for pointing out the eco-stuff, Michael) saver.