The Park tool site is very helpful. This is the best refrence:http://www.bbinstitute.com/index.php. Jobst Brandt's book the Bicycle Wheel is a good learning tool, but I prefer Schraner's The Art of Wheelbuilding for the spoking method.
Experience and the fact that bicycles are simple machines make working on them easy. The only problems stem from the lack of lasting standards and the constant new and imroved stuff that hits the market.