This is a specific game thread, so you probably want to use the pinned thread, or make your own thread.
Anyway, on to your question:
The easiest way is to make a new "ghoul" race, or to simple apply all the effects ghouls have as traits (including undead traits, which are listed here http://www.d20pfsrd.com/bestiary/monster-listings/undead ignore the features, those would be up to your class).
Keep in mind ghouls need to eat flesh in order to not decompose, in the lore, kind of like flesh-vampires. You would need to think of some system to make that work. In the game I play in as a ghoul, we decided that the "race" won't have any penalties to attributes to begin with, but will go with a -2 CHA and -2 STR for every 4 hours in which he hasn't eaten flesh in. If you want to be specific, you could work out a specific amount he has to eat per day to not get that penalty, or something.
Keep in mind charisma is your constitution when you are undead - this does not mean you get any extra points to spend, constitution just becomes unused for anything (or to make things simple, always equal to charisma).
Welp, hope that answers your question