What sort of pattern did you start with?
Did you DL one, buy one or make your own?
Did you DL one, buy one or make your own?
But you could easily add this to almost any pants pattern, so long as the inseam isn't flat-felled.
The only trick is that the inseam has to be open when you add the pocket to the outseam.
I haven't made a paper pattern of it, yet, because I've cut it differently each time. When I settle on a design I will make myself a pattern -- but it'll be pretty specific to me.