First go to the staricase next to the swimming pool, it should have a gate on it.
Next go to the side of it that is againsed the wall.
You then have to jump and crouch straight after onto the flat bit of the staircase. You can then walk to the top once you are there.
When you get to the top you can jump onto a windowsill directly on the wall to your left.
Then jump onto the ledge ahead of you and it is a good sniper spot if you look round the corner.