Letter writing

Listening to Romans this morning, I noticed that Chapter 11 seems to be the end of the letter... and then Paul takes a 'breath' and launches again. 11:33 - 12:2 
I wonder.... writing in prison....  how long did he sit and ponder?  Did he go back and change or add things?  When did he know it was 'finished' and send it off?

What was it like to encourage and teach others from a prison cell knowing a death sentence was in your future?

Oh Lord, Teach me to number my days
That I might use them wisely for you...

PJ