A simple one you can adapt is Tomie De Paola's illustrated children's book about Saint Patrick called Patrick, Patron Saint of Ireland. I have another book that is a chapter book I found at a used bookstore that is also good for future reference (too late for you to get it this time around I know) - Tales of Saint Patrick by Eileen Dunlop. This book is great for descriptive images.
You might also look at Eugene Schwartz's play The Fire on Tara for a way to
bring the story.
Hope that helps (from someone who is just trying to put the story together myself as we speak),
Lisa