Anna Debbenham – creator of styleguides.io – wrote a book on … Style Guides:
Designers and developers have taken different approaches to putting together their own web-based style guides. This book highlights the various techniques and the projects that have used them. It’s packed with practical tips, whether you’re starting from scratch or assembling one for an existing site.
This book is for people who build stuff for the web and want to make their own style guides. It’s full of techniques, practical advice and examples for both coders and non-coders.
It’s in my library, waiting to read 🙂