Junior-
I know putting a bunch of 36" T5 retros sounds like a good idea *but*
Cooling is going to be a big issue, killing bulb life/par & replacing 24 bulbs every 5-6 months doesn't sound fun to me. You can install fans to cool them but unless you have an acrylic cover and can duct the flow over the endcaps this cooling method is really inefficient and can be more of a hassle than its worth. Also- The added cost of an effective cooling setup plus the noise from the fans (you can get quiet fans) but the added cost is another negative
My suggestion is this-
2x 36" 10 bulb ATI powermodules
Initial cost may be a little more *but*
* The PM uses spec ballast so your bulbs will last at least 12 months
* Ducted Cooling with 1 super silent variable speed temperature controlled fan per 2 bulbs (fans are inaudible)-Unlike other mfgs that just blow air in from the sides ATI pulls air through the sides & over the endcaps, There are holes in the reflectors (right above the endcaps) that pull air up over the bulb & through the fixture (cooling the bulbs will hinder your par/bulb life). ATI is the only mfg to do this and that is why this is the best fixture on the market.
* Silver coated reflectors
* Warranty on the fixture
* Sleek & low profile, easy to move
Tbone over at RC has a similar setup except he's got the 8 bulb units
Sorry about posting pics in your build thread just trying to give you some ideas-