First, make sure you have 4 people playing. When you start at the lobby, half the players buy the Olympia (500 Points), and the others buy the M14 (500 points). Don't use your bigger guns yet. Just use your 1911 and your knife to kill the zombies.

One person guard the barrier closest to Quick Revive, one person guard the barrier closest to the Olympia, one guard the barrier upstairs, and one guard the barrier downstairs.

When all of you have earned about 2500 points, buy the top door. Now, all of you buy a PM63, but don't trade your big gun. Trade your pistol.

Then go into the room with the paintings. One person guard the barrier in that room, the other the roof hole, and the two others get on either side of the hall.

Now, when you have earned 4000 to 5000 points, buy the next door that leads to the big room. The two with the shotguns buy the MP40, and the others buy the stakeout.

One person should go and guard the blue room, one person go guard the area around the turret and the barrier, another guard the window by the down-stairs, and the other guard the zombies coming from the other two rooms.

Hold on with this strategy until the room becomes too spacious (meaning there is too much room apart from you and the others) and buy the next door (1250 points).

Stay in that room. Do not guard the barriers, leave them. Go guard the gray doors and camp there. That is a good spot, and it should last you a few rounds plus the Hellhounds.

When you need more room, go on to the stage. Do not turn on the power! Two people guard the gray doors, one guard the barrier, and one run around and help people.

Open the next doors that lead outside so you can run around the entire map if you have to.
Now, if you think you are ready, turn on the power. Everyone buy Jugger-Nog. I will leave you here. Leave a comment if you need help.