If the slates you are working with are of the thick, slate look-alike variety, they are applied and repaired with precisely the same methods used for natural slate. Any comprehensive roofing repair book will contain this information. A particularly good book on this subject is "The Slate Roof Bible" by Joseph Jenkins (Jenkins Publishing, P.O. Box 607, Grove City PA 16167. This book discusses repairs at page 277-78, with special reference to the diamond pattern, which use special clips and techniques that differ from slates and asbestos slates that are shaped like natural slates.