I am working on a screenplay based on my book, "Superheroes Inc." The story follows characters i created and used to draw when I was younger. As I got older, I began enjoying writing the stories more than drawing the pictures. I have three books out based on these characters right now, and am working on the fourth. These characters have never been in any other published form, and are not based on anything presently in the comics. It follows Richard Cage ("The Superhuman") and his group of heroes, who work for Cage's company, a "security" organization for people with exceptional ability. They fight crime around the world whenever called. With characters such as these, there are secrets and sub-plots galore, which become issues in later stories They say "write what you know." I know these characters, how they work, how they act, how they feel and who they are. I have enjoyed writing their stories, and as long as I have ideas, I will continue to write them.
That's kind of awesome. I too have a made up world that I created when I was a kid. I wrote about it as well, but decided it was not commercially viable. Still, it is the one piece that I keep going back to. I re-write it first before I work on anything else. Good luck with your screenplay!