Get up to the roof easily by looking for the side with a slant. On the second level, shoot about three to four shots to the wall next to the slant. Once on the roof, find the area with the glass. Get to the back wall so you are looking at the glass, where it slants, then run at it. As soon as you hit the slant, jump. This is difficult to accomplish. However, when you are up, you can jump from the top to the small bridge-like place on the side. Make sure you do not stand on the glass to avoid someone shooting it and causing you to fall. From this height you will lose about sixty health from dropping off.