This is for both solo and multiplayer.

First go by the broken down eighteen wheeler with the red gas tank thing conected to it. Then go to the drivers side of the truck.

Turn to where you can see the whole entire map (the main part of the map, it has the long rectangle rusted pipe thing that brings you up to the top of the map).

Then walk to the two rusted barriors with a square platform in the middle and jump on the squre platform.

Face the really big tower that has a pole like thing in the middle. If you look a little bit down you will see a rusted little barrier like thing with a few poles inside it.

Run and jump off the square toward the little barrier and keep holding the LS (walking) button so you can stay on it.

Then move kind of left, but not with the LS button completely left. Do it to where it's in between straight up and straight left.

Then go all the way left until you stop. Press A rapidly then you should be on a building like thing.

There you go, you have a great machine gun spot!