As far as I know making scenario's requires programming and extensive knowledge about how the game works (in deep that is). I know in the past some scenario's have been made, but most of the users who made are no longer part of the ZooTycoon community (they have lost interest with ZT).
One member who know his way around scenario's is an admin right here (Casey) maybe if you contact him (PM) he can explain it to you, but don't be angry if he can't.
Cheers
Bielski