The Tower 900
Take a look at the Thermaltake The Tower 900. It fits two up front in the main chamber, and since you mentioned going air cooled, the rear chamber will allow you to install another 10 on each side; which would bring you to a total of 22 drives if you decide to max the thing out. Only thing is that you would need to purchase additional drive cages in order to reach max capacity, but they're relatively cheap direct from Thermaltake. You also get the added benefit of having the bulk of cabling confined to the rear chamber and totally out of view!