Barb's book will help, but a sett refers to the Tartan plaid only, it is the width before the plaid repeats. If you are using a non-plaid, just design it as you like it.

Barb's book is well worth the price, it gives great information. There will be another book that is planned, but not completed yet for non-traditional kilts. Another highly respected member of the X-Marks family is writing it.