It's hard to address your needs because you haven't described what you're looking for in a PC. Builders do it themselves so they can tweak each and every component in the system and because it's good to know what's IN the system when you are troubleshooting or OCing. If you are relatively new to computers in general, don't worry about it and buy one from Costco - you will get a relatively good deal on your machine and great warranty support from Costco. If you REALLY want to customize, you can try Alienware, Falcon Northwest or Voodoo PC to name a few (not sure on their reputations, though). Personally, I'd suggest you build it yourself if you have the time and inclination because you will learn something in the process and you will be able to fix your machine when you are done.