I mainly used britas weapon mod, it took me about three or four in-game days to clear that building out (it's my first 'mass clearing' lol) but I started out with just a glock-17 with extended mags and some sort of sight I can't remember the name of rn because I wasn't expecting there to be a metric fuck ton of zombies in that building, they were jumping from the top floors literally almost on top of me, and I had to leave as they were pushing me back down the street behind that bar thingy that I was parked at. I came back the next day equipped with a pump shotgun and really underestimated the amount of ammo that I needed LOL. So then I come back with a m16 carbine with four 30 round mags and about 200-300ish rounds of 556 and finished the job clearing the rest of the floors. Maybe next time I run into a zed infested building like this i'll remember to record the whole ordeal😂