You don't have to build your own if you don't want to
The absolute best option is to choose a reputable local builder. Someone with a shop and a rep, that supports many small businesses and can back their work with a warranty.
Take such a builder a list of parts approved by us here, and insist those parts are used. This way you have a local place to take your PC should it develop problems.
As far as the big custom builders, I don't know. Many use Cyberpower
http://www.cyberpowerpc.com/