We're not given much information at all about Ozpin's past. If anyone is willing to take up that challenge, I have a VERY rough outline here. I would write and post it myself, but I'm a god awful writer. Just please PM me about it if you take it up so I can read it.
This story can be whatever length you wish it to be, so don't be concerned with chapter length, or number of chapters. It can start at ANY point in Ozpin's past as long as it is AFTER he is a fully fledged Huntsman. This could be as early as graduation day from the academy you have him attend. It should detail some of his career as a Huntsman to show some of his personality in his younger years, and to show how he got the kind of reputation he has when he never seems to do anything in the show.
At any point in this, it should also show when and how he learned the truth behind some of the "fairy tales" in the world. This will later go on to explain how he created the group shown to know what's going on. There should be a story arc dedicated to how Ozpin enlists Qrow, Glynda and Ironwood. Preferably this story would also "explain" the connection Ozpin and Salem have. Finally, the story should conclude with Ozpin deciding it would be "best" if he worked from behind the scenes and becomes the headmaster at Beacon to train future Hunters to continue the fight he started.
One thing I request about Ozpin, is that the shield technique he uses against Cinder is his Semblence. You can change this if you believe you have a better idea that works with what few facts we know about him. Beyond that, I really have nothing else to flesh out the story with. And that's why I turn to any body reading who actually has a talent for writing to get this story written so it can be out of my head.
