Go to the elevators (by the electricity things), then go up the ladder on the side, then look of into the open air.

Look down a little bit until you see the yellow wood then jump onto it.

Then walk to the other one that is higher then jump, turn right and walk or run to the building.

Turn right then jump onto the thing, get in it, then go to the other side.

Get up on it facing the wall, then walk on the ledge, crouch then go into the window. You will be above an office.

Break the glass closest to you, then crouch and kill! Or you can keep going, just break the glass by the thing you can go onto then climb up, lay down and snipe.