Where can I suggest a plugin

Hey,
I’ve recently had an idea for a wordpress plugin, but I’m no good with PHP so I can’t make it myself.
Basically I want to suggest that a developer make a plugin for the default (kubrick) theme which selects the kubrickheader at random from a folder of jpegs.
So each time someone views the blog, they see a different header.
Anyway, I don’t expect a developer to see this and go ahead and make it, but I would like to know how I could get this idea to a developer.

Kind Regards,
Dwain