You can also take a look at my default values overlay which is heavily commented to help newcomers. It also includes a patch you can imitate to integrate the overlay into the build system properly. (The stuff in contrib/ - such as smbk5pwd - does not have usable Makefiles).
-- -- Howard Chu CTO, Symas Corp. http://www.symas.com Director, Highland Sun http://highlandsun.com/hyc/ Chief Architect, OpenLDAP http://www.openldap.org/project/