// This is just an example, not an actual code, so try to think it logic and evern make more of it.

public OnPlayerRequestClass(playerid, class) { // when the player requests for class selection.
     //other shits
     SetPlayerPos(playerid, lobbyposX, lobbyposY, lobbyPosZ); // set the positions to your lobby position
     SetPlayerFacingAngle(playerid, lobbyAngle); // set the angle to your angle position.
     SetPlayerCameraBehindPlayer(playerid); // it change the camera behind player, but the player spawn button is still available, so you can still choose your class and shit, I recomand to delete the SetCameraPositions and staff...
}

public OnPlayerRequestSpawn(playerid)  { // It is executed until the player choose his class. 
    SpawnPlayer(playerid);
}

public OnPlayerSpawn(playerid) {
   // your class functions and other things you want
}

#define Lobby 7