Take a book that is in the public domain, re-set it, and keep a dated record of every decision that is yours. The reading and the finding can be done for you; the deciding and the wording are recorded as your own.
Start from a public-domain book
Project Gutenberg number (the number in the book's address there — The Wonderful Wizard of Oz is 55).
Scenes in this chapter
How the chapter divides into scenes for filming: which paragraphs each covers, and so which pages. Recorded as yours.
Report of changes from the source
Key changes in this chapter, who made them, and how. For internal records.
My creative decisions
The standing choices that shape the whole adaptation, in your own words. Each is dated and kept in the record. Anything drafted for you is drafted from these.