sorry, i cant help but i can give advice in case you dont get anyone as i did it myself
do it on easy, it may take like 3 hours but if your by yourself you have to (unless you major pro)
stay inside the building as much as you can, the enemy come to you and the brute chieftans have a hard time getting at you
use the offices, the glass provides good protection if your health is low as grav ham dudes n drones dont really go in them
good luck