On High Rise head to the back of the helicopter and look at the back of it.

Then go to the left and go down the stairs. Then turn to the left once you are down the stairs and turn left. Go up to the ledge and jump up on the tiny ledge at the edge.

Then look down and you will see a small wooden ledge going around the building - jump on it.

If you want to get back up then is like a scafflin that is broke down, so you can get in it and get back up.