I am just finishing up on one. You can save a lot of money by building it yourself. Plus, you can build in special features that one might not otherwise find. For example, I built in a drawer to make it easy slide in the contact printer, etc.
Here are some tips I would offer.
>> Based on Photographers' Forumlary's design, I spaced my tubes at 1 3/4" centers, using the T12 BL tubes. If one keeps the contact printer at least 2 3/4" from the bulbs, then the light is sufficiently even across tubes. They told me that these distances were based on testing conducted by Dick Arrantz.
>> Price out stuff before you begin to build, looking for reasonably priced online stuff. I used a local retailer, and this probably cost me about an extra $75 to $100. Still, I had the advantage of asking their advice.
>> Get the BL tubes, not the BLB. Not that it makes that much difference, but I read on this site that the BL tubes provide more light in the right wavelenths. Also, consider getting the T12 tubes, not the T10 tubes. The latter are thinner and will require more tubes to obtain the same distance between tubes. On the plus side, this results in greater light output, I would think. Plus, there's talk of phasing out the T12's, but that won't happen for quite awhile.
>> Connect all housings of the ballasts to ground.
>> If you want to turn it off and on, consider having the fans on a different circuit, so the fans can be left on all the time. I used three 120mm computer fans placed along the length of the tubes. It's easier if you get the 115 volt fans, so that you don't need to splice in a 12 volt DC power source. Better cooling with the larger fans.
>> Sort of by accident, I ended up getting separate, smaller ballasts, one for each tube. They also didn't come with starters, so had to purchase starters and corresponding sockets separately. I was told that with this arrangement, I would probably get longer ballast life. It was more expensive, though. It was quite a project lining all these up and doing the circuitry for each. I drew lines, used different color wires for each task, etc. I also purchased connectors to make it easy to remove a ballast, if they go out. It's possible to get ballasts that can each accept two tubes that have internal starters.
>> If you want to do 16x20, consider putting the 16" width along the 24" tube. There's significant fall off within about 3" of the tube sockets on each side. I used 15 tubes, which gives me about 25" of light along the 20" width of 16x20.
With all the time and work I put into this thing, you couldn't pay me $1000 to do another one! Now that it's done, I have something that's better than anything I could have purchased that uses fluorescent tubes.