31 with only 3 people, tomorrow my cousin will be back from his vacation and join us and we should be able to reach higher rounds (he's the best headshotter of the group lol).
I don't agree about the balcony btw, it's not a waste of ammo.. 3 people camping there near the back of it (where the mistery box spawns) can easily handle it, they only come from in front of you so it's really hard to screw up.. we keep 1 people standing in the very back of it and two crouching a few steps ahead, if things are getting out of control you just toss a monkey bomb downstairs which gives you time to reload any weapon (before you get speed cola) or revive if needed.
Edit: of course we only shoot ahead on the balcony, we don't shoot at zombies while they're running in the courtyard or downstairs, that would be a waste of ammo indeed.
I'm thiking the 4th person shouldn't stay on the balcony but on the tunnel downstais instead, as it's easy to control that one window and help weaking/killing zombies from there (and they all head upstairs so you're safe), also the one person standing there could easily keep a crawler each round (keep one alive behind the window) which would make it even easier.
But this is something I've yet to test, will try it out tomorrow night.
About max ammo.. that's the only pain, really. After a while the teleport trick doesn't work for us anymore, it doesn't hand out bonuses anymore or spawns dogs.. then maybe after like 10 tries you get a bonus and then it's dogs or nothing all over again
Yesterday we finally lost at round 31 because we were low on ammo and my friends died, I managed to jump down and port but I quickly ran out of ammo, I tried porting a few more times while dodging zombies (and using the electric trap to weaken them) but I obviously didn't get ammo, so in the end I endep up running around out of money and out of ammo till they ganked me lol.