Get a police car and then get three homies to come with you, put them in the car and the got to Lopeze's mansion.
Across the street will be a hotel, go to the side of the hotel and try to ram the car into the wall around where the can is on its side.
Move back and forth until your car can get some momentum and then move the left analog stick to the right and you should be going up.
When you get to the top press Y to get out, but don't touch any windows or you will fall.
Note: I don't know if it works with any other car but I know it works with a police car.