Here's what I do, I go around the LEFT side of the building, I get on the helicopter platform, then I snipe the 2ND last guy, then the last guy appears and he's running towards me, and I just shoot him.
The problem is people sit on their computers all day before the game is launched, reading about it and building it up in their heads to be something that no game can be.
Hrmm maybe you just need to improve your driving skills since you've just begun the game?
It was extremely easy for me, you just go left once you get in the car and up a few streets.