The Mechanisms and Mechanical Devices Sourcebook, Neal Sclater Editor, has one good page on design of ratchets. Earlier editions of this book are free on the internet, but probably not authorized. The latest edition is the Fifth, 2011. The earlier versions have the same page for ratchet design.
If you are willing to pay for a membership, Engineer's Edge has an article on ratchet design. I haven't seen it but it sounds good:
This section of a book gives you some high level information but doesn't get into formulas or dimensions. Not sure how much detail you are looking for.