I have more experience with Visitor scripts but I guess they're pretty similar (just terrain related stuff instead of model). It was years and years ago though so don't really have any recollection how it worked.
The best way to figure stuff out is to go through the BIS scripts.
The dialogs-demo.bio2s shows pretty well how to build a dialog for your script input (it's a bit odd part of the language because every command must be in an array).
There seems to very little information on the language floating around, I guess you could find something at Bohemia Interactive forums' Arma and Arma2 editing sections, in form of user made scripts