That's a tough question.
If you look at natural bodybuilders none are that HUGE. If you're looking to get HUGE then you'll need a little "help".
But if you want to maintain eat a lot of meat with little fat. No sugars and only good carbs, (fruits and vegies).
If you want to add muscle size the first thing you do is increase weight and slow down reps. That will make the muscle build to help lift the muscle. Then eat really good protein close to right after your workout. When the blood is still rushing in your veins. Lastly train smart. Don't over do it. Some of the biggest guys in the sport only hit one muscle group for an hour once a week. Now they hit hard so don't pussyfoot around.
I'm sure other guys have their opinion, which is good. The more you read the more you can adjust to YOUR body. Everyone is a little different experiment for a few weeks/months and see what happens.