It also could hold up to about three drives, depending on your case size. Of course with more drives in the bird-house, the drive temps will rise, or you will have to increase the fan speed.
The first thing to do if you want to build one......measure your available space carefully, very carefully. Leave enough clearance so the drive connector cables won't touch the case. If the cables touch the case panel, noise will also be transferred into the case....not good. Also....be certain the fan end of the bird-house will clear any motherboard cables/connections.
This whole setup can be easily modified to suit your own needs. Sizes, materials....anything goes. The end result is a quiet drive mounting method, which does not interfere with your ability to cool the drives.
A number of people have posted pictures of their own versions of the "bird-house mod"......check them out.

Most of the photos from this mod have been moved to this PhotoBucket album