Rounds 1-4
Just knife and shoot the zombies with a pistol.(dont buy a gun in the lobby). Once you start getting into trouble open the next two doors at the top.

Rounds 5-8
Once your in the mp40 room, buy the mp40 off the wall. Everyone but one person watches a window. The other person watches the door. After dogs come, buy to the stage.

Rounds 9-10
Turn on the power and have everyone buy juggernog. Open to the alley way from the stage and the open the gate. Dont open the door by double tap.

Round 11-20
One person watches the window while everyone else watches the alley. Every round you should keep a crawler so you can buy new guns, upgrade, etc.

Round 20+
Everyone should have all the perks, two upgraded guns, and should have a good amt of points. Now you can open every door and run around together setting up electric barriers, turrets, and every round going into the teleporter. At the end of each round when there are probably a hundred crawlers everywhere, i suggest knifing them for it will safe a lot of ammo and get you a ton of points for traps.

HOPED THIS HELPED!