Is it a good choice to adapt a project as an unproduced writer – or should you concentrate more of your energies on writing your own original screenplays?
I actually discourage new writers (i.e., unestablished, without credits) from writing any screenplay to which they don’t own the rights.
The problem with then adapting something as an independent (i.e., not getting paid by a producer or company who already owns the rights and has the project in development) is that you will likely acquire a limited option to the rights of the material.
So, let’s say you can get the rights and negotiate and pay (or not) for a two year option on the material. You take several months to write the project, say, up to a year, then you get a year to shop it. If nothing happens within that time and your option lapses, then the original writer will possibly have more choices, will be on the radar of more people, and if they feel staying with you isn’t in their best interest, the option will lapse, so will your rights, and now you’ve spent a year working on something that won’t serve you.
To this end, I think it’s always best to have an arsenal of material to which you own the rights. That way, if in five or ten years you want to take something off the shelf and brush it up, you can.
There is actually another issue at hand here. Screenwriting has a lot to do with being facile at pitching ideas and the trade of ideas. It’s important to actively cultivate your own skill at generating and working with ideas. You should be continually harvesting information that could generate story and character and then play with the applications of that material in ways that are specific to screenwriting.
For example, you might practice taking a basic high-concept premise and playing with story and structure in different genres, just for the sake of seeing how that idea would develop in different directions. Or you might see someone on the street that inspires an amazing protagonist and apply that character to various situations and genres.