At the Poisson map, there is a barn or house behind a Nazi Tiger Tank spawn. 
This part of the map is the part where the Nazis generally respawn. Go in 
and there should be a ladder. Climb the ladder, then walk over to the window 
in the front. To your left should be some boxes. Back up. Get prone and 
crawl up to the corner on the left side of the boxes. Crawl until you cannot 
move further. Then, stand up. If done correctly you should be apparently on 
top of the roof. Although you cannot move, you will have a great sniping 
position. If you prone again you will be back inside the house. You will 
also have a great view on the little town area and the road to the right 
that leads up to the house that is next to the other Tiger spawn point.