[kovac]

In server conf:

gamemode0 grandlarc 1
gamemode1 other_gm 1

PHP код:

new bool:Voted[MAX_PLAYERS];
new Votes;
CMD:vote(playerid)
{
    if(Voted[playerid]) return SendClientMessage(playerid, -1, "ERROR: You can vote only once.");
    Votes++;
    Voted[playerid] = true;
    
    if(Votes == 5)
    {
        SendClientMessageToAll(-1, "5 players voted for next gamemode, changing..");
        SendRconCommand("gmx");
    }
    return 1;
}
// OnPlayerDisconnect
Voted[playerid] = false;
CMD:votes(playerid)
{
    if(!IsPlayerAdmin(playerid)) return SendClientMessage(playerid, -1, "ERROR: You are not RCON admin.");
    new string[128];
    format(string, sizeof(string), "There are currently %i votes", Votes);
    SendClientMessage(playerid, -1, string);
    return 1;
} 


Untested.

EDIT: I misunderstood. I thought that you want to change the gamemode. Sorry. Anyhow, the principle is similar, you can figure it out.