Here’s a simple tip for you: don’t adapt a screenplay from an existing story without first acquiring the legal right to do so. This could mean a book that someone has written or just a story that you saw on the news. If you don’t have a signed document giving you the exclusive rights to adapt another person’s story, then you shouldn’t write a single word of it. If you do write an unauthorized adaptation like this, no studio will touch it because you are only creating a legal nightmare for them. Then if you decide to produce the film on your own, either it will be popular and the original owner of the story will sue the crap out of you, or no one will see it and you probably won’t hear from anyone about it ever again. Neither of those is a good option.
See what I did there? I used the word “option” to segue into the topic of how to acquire the rights to a story, which is to get an “option” from the original copyright owner. I’ll go ahead and stop putting the word “option” in quotes now. Here is a good source for information on how options work and why you need one:
If you’re not sure what kinds of works need an option and what qualifies as fair use of an existing work, here’s an excellent site that should answer all of your questions:
So how can you acquire the rights to someone’s story? Even if you’re not an established screenwriter, your appreciation of and passion for another author’s work might convince him or her to give you a cheap or even free option for a relatively short amount of time to see what you can do with the story. It’s definitely worth a shot and the worst they can do is say no, which is definitely the kind of answer you want to receive before dedicating several months of your life to a project, rather than after.