Well I have just been through the exercise of building my own cabinet, I have an alcove which I wanted to install a cabinet into.
I ended up using 3 racks similar to the mid atlantic
[Link: middleatlantic.com] these wer built into a cabinet that had 3 sections made from Tasmanian Oak. There is plenty of air ciculation with inlets at the base which is filtered. The top of the cabinet has a depth of 700mm (29") and has a book case built onto the top. There is about a 2" gap between the wall and the back of the bookcase for the warm air to rise, this is also filtered to stop crap from falling down.
Only took me 6 months from start to finish to build the cabinet and bookcase.
All the cabling was custom made between the equipment.