Go where the turret is in the building that is not blown up. Climb on the ledge of the turret. Look to the right and hug the wall tightly while moving forward. Once you go a very short distance onto the invisible ledge next to the shutter, run
and jump onto the roof ledge in front of you. Look to the right and jump through the shutters. You will be in a room where you can see out from, but other people cannot see you. Note: You must climb on the window ledge a certain distance to shoot out and throw grenades.