Be careful as you may need to land using the fire extinguisher to not die of the fall damage. Go to the top, enter the building and take all of the items. Go outside and go to the big red building on the right side of the map. Open the gate and the red door using the silver key.
You don't need the silver key anymore so throw it away as you will need more invenory space. Go the building next to the opening gate with a funicular hanging next to it. Instead of entering the building, climb up the 'stairs' and jump one the bent red-brownish fence.
Jump into the hole in the floor next to the door and pick the generator up. Return to the cafeteria (the red building).
