Lasers, snipers, and BRs can shoot through fence walls, and I found out how to make the chopper immobile. Place the chopper (preferably on a raised platform, place a sign A/B in front of the chopper's wheels, with the end that is normally placed on the ground facing the chopper, then use one window, and one sign placed on the back to trap it (alternatively, you could use two windows, but the player occasionally gets trapped that way). If the zombies have normal shields, and 50% damage resistance and humans have 110% damage, the plasma pistol kills in about 6-8 hits (which can be achieved in 1 second). I've played a few games on this and the people that I played with said there are no balance issues. But if you like your version better, enjoy it.
You obviously don't understand it. The zombies need to work together and strategically to avoid ever getting shot. There is a big wall of telerporters where they could come out, and once they do, they can easily stay alive if the humans aren't good, if they rush in a group, strategically use a zombie powerup (any zombie could get any of the powerups any time they spawn once you get about 20 seconds into the game). This map is a change from all those basic zombie games where there's one entrance to many different places, and zombies just walk up and get killed. The zombies can easily stay alive through using stategy and teamwork, and the humans must do the same to stop them. It's actually a little bit easier for the zombies. I didn't know laser can shoot through fence walls, that could be a good change then possibly. I wanted the chopper to be mobile though, you can use it to splatter to try to survive if your the last man standing.