Haha, I think this is a lot of fun. Last time I climbed up on a roof after a particularly bad run in with a sniper and some walkers. I had 2.3k blood, and kept falling unconscious. I had food and water, and some ammo for my shotgun, but it was grim. I had no knife, so my only hope was to find some other person in town. (I figured this was a good idea, since there was probably someone else that needed blood, right? :P). So I manage to pull aggro in the city, I've climbed onto this roof, and I see this guy down below, I shoot some zombies to make way between him and me, and keep shouting: "Up here! I need help!". Of course, once he had a clear path, and gets to the building, he just shot me in the head, but at least there was the possibility of us sharing two blood packs. :) I am glad not everyone behaves like that fellow.