The various pickups on the lower level of the building are covered in the main walkthrough. When you have everything, exit through the open door to the northwest.
There are 4 more enemies at the top of the stairs on the left. If you go quickly you can shoot the fuel barrel they're about to roll down the stairs...
...and kill one or more of them in the process.
Then take out the spotlight so you can see what's going on.
Shoot the others as they come down the stairs or fire at you from above.
One has armor and a pole arm. You can hit him with a couple of grenades (aim a little above his head so the grenade doesn't fall short).
Or, blast away his armor as he approaches (as shown above). Otherwise, wait for him to come to you and kill him with a Dodge Counter maneuver.
As you fight him, another guy slides down the ropes in the previous area and sneaks up from behind. So watch out for him. Better yet, try to take out the pole arm guy quickly. Then run back out to the previous room...
...and shoot the sneaky guy.