Spawn on the side with the big "KREIGLER" letters. Go to the other side of the "KREIGLER" letters. You will see a hanging window washer container. Jump off the map towards the container, and land on it as if it wa ladder. Wait for a moment and make sure your character is attached to the container. Move up (as if climbing a ladder), then walk on the scaffolding to the other side of the building. Jump into that container, then onto the roof. You have now successfully made it to the roof. It is best to have a tactical insertion when playing in multi-player mode.