On the Marine/S.A.S side, climb up the ladder to the building with the sandbags on it. Jump onto the lamp post. Sprint jump at the blue radiator on the roof beside you. Keep tapping X, you will get on the roof.
On the OpFor/Spetznas side, countersnipe the three story building. Go into the building beside your spawn point. Go onto the brown balcony. Looking across the street into the garage, go left on the balcony to the edge. Stand on the railing and look directly in between the two buildings. You should be able to see most of the three story building's roof.