It's pretty similar to your other post wink
Check if $nick isop, then use $rand() and $nick(#,0)

Code:
on *:text:!giveaway:#:{
  if ($nick isop #) { [Giveaway]: $nick(#,$rand(1,$nick(#,0))) Just won the giveaway, we'll send you a message with details on how to obtain. }
  else { [CMD]: Dear $nick , You do not have permission to use this command! }
}