Ok, here's how i would do it:
Code:
On *:text:!giveaway:#:{
  if ($nick == YOURNAMEHERE) { msg $chan Giveaway started on #, type !enter to enter $+
    write -c Raffle.txt
  set %rafflestatus ON }
}
on *:text:!enter:#:{
  var %f = f. $+ $ticks
  .fopen %f Raffle.txt
  while ($fread(%f)) {
    if ($nick == $v1) { .fclose %f
    return } 
  }
  write Raffle.txt $nick
  .fclose %f
}
on *:text:!winner:#:{
  if ($nick == YOURNAMEHERE) {
    if (%rafflestatus) { msg $chan $read(Raffle.txt) is the winner $+
      unset %rafflestatus }
  }
}


Maybe someone can improve this.