This is the former storage that is currently being inhabited by gunners or synths, depending on your character level. You encounter them both outside and inside.
Search the main warehouse thoroughly. You find there lots of ammo and meds hidden in several spots.
In one of the rooms at the first floor, on the desk, you find an issue of Picket Fences and a key to the storage.
The storage is at the end of the corridor as the room with the key and it is normally locked with an advanced lock. Inside, there is a master-level safe, a Stealth-Boy and some ammo.
In the main room, there also is a paint mixer, where you can mix the yellow and the blue paints to obtain green, which you need for quest Painting the Town.