I second dgaddis on that. It’s almost always better (cheaper) to buy a complete bike than to custom build. The biggest reason is the fact that the manufacturers have volume purchase power and are able to get the components at a lower cost than most retailers. Thats another reason the big online shops can usually sell at lower prices than an LBS. On a side note buying from your LBS helps small businesses and allows you to build rapport with the owners and staff which may come in handy.
Also, when buying a complete bike it’s also better to scrape up a little more money and buy the best bike you can afford as opposed to buying a lower tier one and planning to upgrade the stuff later. Theres’ nothing wrong with doing that but it is more cost effective in the long run to buy those "upgrades" up front.
Of course if you just want that custom spec, building up your own ride can be a fulfilling experience and may be worth the effort of bargain hunting and such if you enjoy that type of thing.