I went to a Buccos/Cubs game a couple years ago. Sat in rightfield with the bleacher bums. Had a very good time; can't remember how early we got there, they were doing batting practice so it was probably an hour and a half before the starting time. Of course it was the Pirates in 2009 AND it was early July so yeah you better get there real early, especially if you're with a large group of guys (we had 10).
Rooftops are too far away imo. I just think the novelty would wear off after the 1st inning.
After the game I suggest Sluggers Bar and Grill. They have batting cages upstairs. Good times.