If you have a huge room but a not so huge light source, I would recommend putting mylar sheets or something similar to sectionoff a part of the room. This will concentrate the light and put it where it's needed and not lighting up the whole room. You probably already have something like this, but it will help a lot to maximize your light. If it isn't a small sealed place, like a tent, ventilation isn't as critical but you might still want to have some sort of exhaust system as things can get pretty stinky towards the end. Good Luck!!
Personally, if I had an large area like that with a relativly high cieling, I would grow some bigger plants since you have the room. Maybe next grow, upgrade to a 1000w bulb/ballast and grow some monsters indoors. I sometimes get 7 ft indoors with huge colas, but it depends on the strain, since a lot of new strains are pretty short, along with autos. A few 6 ft indoor plants are pretty impressive.