[Soumi]

Put all your class's under OnGameModeInit , then you need to place the player Position when he is choosing a class , also you need to set the Camera Position and the Camera look at..under OnPlayerRequestClass..
Here's an example :
When player chooses a class , he's position will be in the desert.

PHP код:

public OnPlayerRequestClass(playerid, classid)
{
    //Teams
    SetPlayerPos(playerid,11.9577,1716.7191,22.6222);
    SetPlayerFacingAngle(playerid, 128.0980);
    SetPlayerInterior(playerid, 0);
    SetPlayerCameraPos(playerid,9.6063,1715.1882,22.6113);
    SetPlayerCameraLookAt(playerid,11.9577,1716.7191,22.6222);
    //-----------------------------------
    return 1;
} 


Also you can add a music and an anim..

if you need more help please let me know !!