every random event has opposite event except earthquake (which happens too often for my taste) so how about event which creates buildings? of course it wouldn't happen if player has fully built land (quite unlikely).

Even if your land was built up, you could have an event like a "commerce boom" that forced X number of buildings to convert to Ent. zones. I like the idea of more random events in the game. it would make it a little more interesting.

Why would a fully built techer/farmer/indy want a "commerce boom" that would "rainbow" him by building Ent. zones?

techer etc doesn't want eqs either.