He said that phase transformed him completely from an "aimless slacker boy to a worthy person".
"I have not thought about it (writing a book) at all. I have miles to go before I can think of something like that," the 32-year-old actor told reporters at the launch of cover of Ronnie Screwvala's book Dream With Your Eyes Open.
"But if I had to, then it would be the time when I assisted Mr Bhansali on Black, because that was the time I really switched from just being an aimless slacker boy to somebody who wants to do something in his life related to films," he added.
Before foraying into acting with Mr Bhansali's directorial Saawariya (2007), Ranbir worked as an assistant director with him. Although the film didn't fare well at the box office, but Ranbir was noticed for his performance and he bagged Filmfare's Best Male Debut Award.
Further, he praised the National Award winning director and said, "He was a great mentor, a great teacher, so to write something about that would be interesting."
Meanwhile, Ranbir is waiting for the release of his film Bombay Velvet, which is directed by Anurag Kashyap.