Ive always thought the attic was the best place to start.... but i know how hott an attic can get. If you have hot summers and such it might be a bad idea unless you know u can keep the area cooled to atleast 80 degress. You dont need to drywall, you can get some white tarp and staple it into place and duct tape the seams, all u need to really do is cover the walls u dont need any support like a drywall, esp for an attic. Make sure that heat will not become an issue before starting... u will be very dissapointed if you cannot get temps below 95, and thats not that hott for a summer attic which can get up to 110 degress on a 90 degree day just from the sun on the roof.