Act 4: The Long Road Home - 6. The Siege
All the ammo is back in place to pick it up as you make your way to the second story window (Frags in the room across the Emergence Hole). When you meet up with your friends you should take cover. There are four Drones and a lone Theron on the front side. Try to lob a few Frags down there, but you probably won't take them all out. So just pop and fire while in cover. Eventually, a Boomer will pop up, but he isn't trying to kill you, he will suicide to the front door and blow it apart. You can try to kill him, but I couldn't do it with all the guys below. Just let him go and keep taking out the others. The Boomer brings some more guys, and after a while you will hear a Theron bring a few more. Also, there will be a regular Boomer after the other one. All I can really say is that the reinforcements come from the openings in the wall. Once you feel like you've killed as many of the guys from the third wave as were in the front, then switch to killing the few enemies that are in the house.
Collect all your ammo anywhere and then the Frags in the blown out room facing the front. Then go down the stairs for yet another surprise, this time from the door by the stairs, so get the chainsaw revved up. Go through that door keep going (there are some crates and Frags along the way, but you shouldn't need it). When you burst through a door, get a Frag out, go to the window, and throw the Frag before those guys crawl out of the hole; the hole opens behind the big statue/art thing. Then kill whoever remains, and once the fight is over, shoot for the propane tank by the door across the way to blow away the boards holding the door closed (no point telling you to open it if you can't).
Go back, pick up ammo (some is under objects), and go through the open area. Kill the lone Drone and then go to the next open area. Quickly get to the railings with your Longshot in hand and aim to the area in front; get a shot in on one of the Boomers and then take cover. Just keep taking popshots at the two, you only need to hit each three times. Once that is done, Roadie Run as far as you can in the APC's direction (where the Boomers came from). When you poop out, don't try to fight or close the hole, just keep going; dive if you have to.