if(response)// They pressed the first button.
    {
        switch(dialogid)// If you only have one dialog, then this isn't required, but it's neater for when you implement more dialogs.
        {
            case DIALOG_CLASS:// Our dialog!
            {
                switch(listitem)// Checking which listitem was selected
                {
                    case 0:// The first item listed
                    {
                        SetSpawnInfo(playerid, 0, 0, -546.0, 2594.0, 54.0, 270.0, 0, 0, 0, 0, 0, 0 );
                        SpawnPlayer(playerid);
                    }
                    case 1: // The second item listed
                    {
                                SetSpawnInfo(playerid, 0, 0, -379.09, -1445.18, 25.72, 180.0, 0, 0, 0, 0, 0, 0 );
                        SpawnPlayer(playerid);
                    }
                }
            }
        }
     }
     else return Kick(playerid); // if he didn't choose the first button, will kick him.

new RandSkin[][] =
{
    144, 145, 146, 147, 148 // On script's top. Here are the skins number you want to randomize.
};

public OnPlayerSpawn(playerid) // You may change it for any callback you want
{
    new rand = random(sizeof(RandSkin));
    SetPlayerSkin(playerid, rand);
    return 1;
}