Like the WJG (wall Jump Glitch) This is done the same way only instead of a wall it is done w/ a roof. first WJG as high as you can go in just about any level. once you hit the top of the level or the roof just turn away from the wall and hold forward and keep jumping. just like the wall you should stick to the roof and be able to go across the level roof until you are over a building w/ a roof. I have personally done this in Manhattan,Tampa, and Vancouver. some times however the roof isn't straight across you may have to drop down a bit to keep going.