This works on any mode.

Go to the small wooden hut near the centre of the map, when you exit this hut there is a white skip or trash can in front of you.

Climb onto this and then up onto the wall, when on the wall, turn left and head for the centre building,.

Just before it, sprint jump onto the edge of the roof.

Once up here, you can walk anywhere on the roof and can walk along the fences to the building near the stone bridge.