#define TEAM_1 1
#define TEAM_2 2

new Team1 = 0;
new Team2 = 0;

public OnGameModeInit()
{
  AddPlayerClass(...); // Team 1
  AddPlayerClass(...); // Team 2
  return 1;
}

public OnPlayerRequestClass(playerid, classid)
{
  if(classid == 0) { SetPlayerTeam(playerid, TEAM_1); }
  else if(classid == 1) { SetPlayerTeam(playerid, TEAM_2); }
  return 1;
}   

public OnPlayerSpawn(playerid)
{
  if(GetPlayerTeam(playerid) == TEAM_1)
  {
     Team1 ++;
  }
  else if(GetPlayerTeam(playerid) == TEAM_1)
  {
     Team2 ++;
  }
}
public OnPlayerRequestSpawn(playerid)
{
  if(TEAM_1 > TEAM_2 +1)
  {
   SendClientMessage(playerid, 0x000000, "Team is full, choose the other");
   return 1;
  }
  elseif(TEAM_1 > TEAM_2 +1)
  {
   SendClientMessage(playerid, 0x000000, "Team is full, choose the other");
   return 1;
  }
  return 1;
}