I think I had a process for building a shop from scratch on here, here's a link with basically the same info. It may not go into too much detail about how to build the exposure unit but it might give you an idea of how we did it in Tim's garage. It was fairly easy and cheap and works great.
I have my fixtures about 3" apart, I think? And I've seen some as far as 6" apart too, anywhere in that range should be good. I'd keep the light about 6" - 8" below the glass too and you should be fine.
Here is what I built. Everything but the bulbs were from the Restore (thrift store for building supplies). It was about $150 for everything. Whatever you build, use an exposure calculator. Makes life easier. http://i.imgur.com/R3N9G.jpg
I think Jeremy Wilson and maybe some others added a vacuum lid to theirs - 3mm close cell neopreme used in wetsuits, attached to the bottom of a hinged frame that sits and clamps (eyehooks or similar) to the bottom section, and a valve made from pvc pipe you can hook a vacuum cleaner to.
If you notice visible thick and thin waves on your emulsion after exposure and washout, you need to (a) move the bulbs closer to each other in an evenly spaced pattern, or (b) move the bulbs away from the glass. or a combo of the two. We use 'super actinic' bulbs in our factory made units, they work pretty well (Delicious Design, Black Swan, Caughtin Customs, Burning Bones Press, John Brown University, Ryan Burkhart all have these flourescent UV bulb units)