Step 1: Check if the user is an op
Step 2: Check how many users there are in the channel
Step 3: Random between 1 and the users
Step 4: Print the user
Code:
on *:text:!roulette:#: {
if ($nick !isop #) return
var %users $nick(#,0)
var %user $r(1,%users)
msg # %user is chosen to play roulette. However you do this is up to you. 
}
As for Step 5, I'd recommend transforming your current roulette script into an alias passing # and $nick to the alias, that way you could do the same with this script, passing # and %user to the alias.

/help aliases


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Nillen @ irc.rizon.net