Spawn on the side with the big "KREIGLER" letters and go to the other side of the "KREIGLER" letters. Notice the hanging window washer container and jump off the map towards the container, making sure to land on it as if it was 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 and onto the roof. You have now successfully made it to the roof. A tactical insertion when playing in multiplayer mode is recommended.