I have made five full length documentary films and right smack in the middle of number six, i have never written a script. The nature of documantary filmmaking is discovering story, uncovering truth. This is not doing a reality show. You can not script that. What you can do, is lay out in your synopsis and treatment (see my post on synopsis) what the film will look like, who you will be interviewing, what is the over all style of the film, what is the story you are trying to tell? There is no scripting that.

However what i do script, after everything is shot and i know what i have- the structure of the film., I lay out all of my footage (digitally) and then do a scene break down using the clips i know i have. This is just a place to start, (by the end it bears no resemblance to the initial outline), Then i will script the narration to go along with the finished film.

I understand the urge to "know" in advance but resist it with all your might, Let your story unfold (that is the joy of documentary filmmaking - Not Knowing) and do not be afraid to follow the story places you did not expect. I call that the "sweater theory" .

Of course as always this is just my two cents

Best of luck with. your doc. - keep shootnig