OEM PCs were so much better about 5-6 years ago compared to now. I have an old Gateway Pentium Pro 200 system that has never had one hardware failure, and it was pretty stable with Windows 95(which is a damn hard thing to do).
I think in the last two years or so they've really gone downhill. Going with cheaper and cheaper components all the time. For instance, when a manufacturer's PSUs are rated for less now than 3 years ago while power requirements have gone up, that's a problem. Not to mention how many dead components my parent's last Gateway had.
If your roommate isn't confident in building his own, I'd definitely recommend a local shop. Just talk to them, and explain that you are choosing them over an OEM manufacturer because they did really good work. Should not try to screw you too much on the price, but it will cost more than if you built one yourself.