I had the good fortune of being able to follow a one day course on wheel building last year and built wheels for my 29er this year. Very rewarding, but it is a very involved process where lots can go wrong. On the other hand, people call it a black art, which it isn't , its just complicated. But as seen in other comments, there are several good tutorials to start with. Freespoke is a good site with info on measuring rims and hubs, a spoke calculator and a comprehensive list of hubs and rims.
But there is no shame in paying a pro to build a good wheel. In NL, where I am located, there are several webshops who offer the service and I have used them in the past.