The Homeschooler's Guide to Portfolios and Transcripts by Loretta Heuer, M.Ed. is the book for you.
Heuer is a former classroom teacher who homeschooled her two sons from pre-school through high school. She has been the legislative liason and electronic information coordinator for the Massachusetts Home Learning Association and has spoken widely on the portfolio/transcript process.
In this book, Heuer describes the differences between portfolios and transcripts and when each is appropriate. She provides step-by-step instructions on how to collect artifacts and documentation as well as how to organize them. She also provides instruction for those whose homeschool experience has been more unconventional, such as unschoolers.
This book was written in 2000, so some of the information on technology is a bit dated. No one will be submitting a video on VHS tape. However, many of the ideas can be adapted to up-to-date technological offerings. Overall, it is an excellent guide for any homeschooler needing help with providing documentation of the homeschool experience.