Battle ground is wonderfull, but will be good something implement for team balance.
I have a little suggestion:
For example, you cant start game, if the condition wont be:
n1 < n2 = n1 + 1
n1 > n2 = n1 - 1
n1 == n2
n1 - number of people in left room
n2 - number of people in right room
Or similar, later maybe recognition of builds and theirs suitable remove to weaker side.