26.09.2015, 10:58
At the beginning of a race, set a variable to 0. Whenever someone finishes the race, increase the number by 1 and that number will be their finishing position.
To help you understand:
Keep in mind, racepos has to be a global variable! 
To help you understand:
PHP код:
new racepos;
OnRaceStart{
racepos = 0;
}
OnPlayerFinishRace(playerid){
racepos++;
new str[128];
format(str, sizeof(str), "You finished at position %i", racepos);
SendClientMessage(playerid, -1, str);
}