You can actually get up on the roof of the Lobby (where there is the giant skylight) to find a Fusion Rocket Launcher and a Rail Driver, as well as a great sniping spot. To get there, first go up to the second level of the area where you are able to pick up the Rocket Launcher. Next arm that weapon and aim for the corner of the wall where the skylight begins. Fire off rockets to punch a hole into the ceiling and the wall. Continue to fire rockets until you form a small alcove where you can then jump up onto the roof.

Once you are up there, you can grab a Fusion Rocket Launcher at one end of the skylight, and a Rail Driver at the other end.