Attics are cold in the winter and way too hot in the summer- It will be expensive to be cooling air that you're then going to exhaust thru the room. Kinda like having a window open and a fan blowing out while you're running your AC. If you're going to run AC'd air thru, I'd insulate the space and have exhaust return to the part of the house that was climate controlled. I'd also use air-cooled fixtures to dump as much heat as possible, with the intake sucking attic air, and then exhausting to attic air- and you have an attic fan, right?

Really, you'd be better off in the basement. It's really tough to keep an attic space cool, what with heat from the house rising and the sun on the roof all day. Attics are doable, but you need like 3-4 times the cooling capacity.