Code:
on *:text:!rose*:#:{

  ; Set your anti-flood configuration here.
  ; I've set it to ignore an user for 300 seconds (5 minutes)
  ; if (s)he says "!rose" for at least 3 times in 5 seconds.
  var %lines = 3, %secs = 5, %ignore = 300

  var %id = $+(%,flood.,$cid,$site,#)

  inc $iif(!$var($(%id)),-u $+ %secs) $(%id)
  if ($(%id,2) >= %lines) {
    .ignore -cu $+ %ignore $nick 4
    .notice $nick Anti-flood: you're now ignored for $duration(%ignore)
  }
  else { msg # $nick gives $2 a bunch roses showing his/her love. }
}


Please note that I haven't tested the code.