In San Francisco on Cruise, if you take your first left when you cone to a T junction then drive on, there is a building which you can go in. Go in it and go up a ramp and out onto the White roof. Turn around so you are facing the door you just exited. You need a lot of speed but if you ram into one of the bottom corners of the door, then you will start to go up the slanted side of the building. I advise you use an Audi TT to do this or else you won't make it up the sloped roof. This works if you get it at the right point!