Inside the main building, this is the end point for the main game's missions.

On top of the main building. There's a ladder on the side of the building that allows access to this check.

The roof of the opposite building. You can see this location from the other roof, and vice versa. There is also a check inside this building, just inside the door.

There are a few checks on the outer ring of the area, but this is one of the trickier ones to find. This corner is directly to the right of the truck and down the fenced-in area.