When you start, come out of the spawn and go straight (do not go across the zipline).
You will see a gap with a fence around it, stand on the ledge and jump round the fence onto the ledge the fence is blocking.
Then walk on the ledge and jump onto the main roof.
But be warned you can still get shot at, grenaded or droned when standing near the yellow terminal.
To get out simply walk through the fence.