I purchased this online book - very good.
Whilst there is a great deal of myth and 'witchcraft' associated with it, the book really does put a spoke-key in your hand and help you do it.
There are of course many people with a lot of years under their belt who will do an exceptional job, its a good starting point and the few I have done have been an enjoyable experience.
Like most fields, there are some people that are excellent and others that are just plain - I tend to build mine and them take them to my local bike shop who have a good wheelbuilder and get him to check / sort them and tell me where I got it wrong. Its all learning and not likely to make you a millionaire but it gives you a good grounding in fixing them in the future.