Solo:
1) Stay in the lobby until the middle of round 3 just using the knife and not buying the quick revive yet. You need 2750 points to open the next two doors & buy the MP40, you should be able to accumulate that just knifing the first two rounds & killing two enemies in the 3rd. After you have 2750, run to the MP40 room, get the MP40, and come back and kill remaining zombies.
2) Move on to the MP40 Room. Camp out between the bottom of both staircases. You need 5000 Points to move to the theater & buy the Juggernog. Go for head shots!
3) Once you're in the theater & have Juggernog, which should be round 5 or so, run circles on the stage and hoard the zombies. Once they are all together, shoot them w/ the MP40 and walk backwards through the stage.
4) I can usually get to level 20 in less than an hour just doing this with just the MP40, and after buying quick revive/speed reload, you should a hell of a lot of points. That's enough money to hit the box a few times til you get the Thunder Gun. Once you have the T-Gun, things get easier and rounds go faster.
5) Run loops on the stage to accumulate zombies, they stop spawning once there are 25 zombies or so. Blast them, then wait for the next wave to come & repeat. There are roughly 4 waves of zombies per round, I use the T-Gun for the first 3 waves, then slowly kill the last wave with whatever backup gun I have & leave crawlers if I need to.
6) Remember you have 28 blasts w/ Zeus Cannon. I use no more than 4-5 blasts per round to make sure I have enough until dogs come out. It's great if you have a Ray Gun as your back up which you can use for the dogs & leaving crawlers at the end of the rounds if needed.
7) If you're running low on Zeus Cannon ammo, accumulate the zombies so they're all running together, then lead them around the map running through the lobby first. Don't worry about shooting them, just have them follow you. Remember when you kill a zombie, another one will spawn somewhere, likely in front of you. When you reach the dressing room, hit the trap. Now you're back on the stage and you can run your circles again.
Tips: If you're doing the stage thing, keep the teleporter on. If you go down, run straight to the teleporter and hit it. Chuck grenades down, then when you teleport back, carefully make your way through the map and pick up your perks as you go.
Don't waste your time boarding up windows after round 5, it's not necessary. Personally I never use the teleporter unless I go down. My goal is to get through the rounds as fast as possible, and boarding windows and waiting for the teleporter to cool down is a waste of time.
I try to avoid using LMG's, they're great for ammo, especially when you're trying to build points, but not good for this close quarter strategy since they're so heavy and slow you down. Strange thing is the Zeus Cannon is so light, it feels like you're running around with a handgun...
I've gotten to level 32 w/o using any quick revives with this method. Maximum level in solo: 42
