No tut but here's how I do mine.
I cut a circle of cardstock in the size I want my rosette, hot glue the end of my ribbon to the center.
Then I fold the ribbon in half and twist the ribbon tightly around the center a few times and then hot glue this down to the circle.
I then continue to wrap the ribbon around, twisting it as I feel like it, and glueing to secure it as I go.
Then I finish the back with felt.
Wish there was more of a formula for you, but it's really subjective. You can "roll" it more to make it thicker like a rolled fabric rosette, or you can "twist" or fold it over more and roll it tightly together to make a more uniform rosette. Or a combination of the two.
I just start them and see what looks good as I go.
I'm on my phone right now, but I'll post a pic when I get home.
I hope that helped?