If you are staying on the north perimeter, your choices may come down to where are you on the north perimeter, I-75, I-85, or Dead Center at the Perimeter Mall area around Ga HWY 400. Even though the perimeter (I-285) encircles Atl most people when talking about the perimeter area are actually talking about due north which is the Perimeter Mall area. If this is the case, the nicest gym in the area is Concourse Athletic Club. It only has dumbells up to 120 however but has pretty much everything else in addition to indoor, outdoor pool, tennis courts, restaraunt with some reasonable healthy fare. Phone number is 770 698-2000.
There is also a few of the chain gyms in the immediate area but they are considerably more crowded. One that comes to mind is at the Perimeter Pointe Shopping Center that I believe is a LA Fitness.
If you have a car and want to see a better body builders gym, then Main Event in the Marietta area, and Coffee's gym also in Marietta, and Golds Gym in Sandy Springs are going to have more BB types than the others. They are less than a 10 minute drive from the top end perimeter but with traffic that could easily triple. Let me know if I can be of assistance, that is the part of town I live in.
Pekkerwood