This isn't really a cheat but is a good sniping spot.

First go into the building right before the bridge (it's on the side of the barn), go behind the building and there's a dumpster,

Climb onto the dumpster, then climb onto the wall, here you have two choices - you can either go onto the bridge or if you look to the left depending on the way you got up there's a building.

Walk the wall until you get to the end and jump onto the roof.