You can build a "pretty good" PC for less than a mac if you only compare the specs. Once you throw in things like service, build quality, noise level, footprint and intangibles like style, macs own their category. But sometimes pretty good is good enough.
BS. You can build a way better PC for the money than you can buy from Apple.
Service: I can get things done quicker myself, and done right the first time. I can't tell you how many times I've seen PCs get work done on them, only to be sent back exactly the same as when they sent it in.
Build Quality: Like anything you can get cheap parts or quality parts. However I can guarantee you can get a lot better parts then the foxconn ones used in Macs.
Here's a PC I built 2 months ago, 4.5 GHz 2500K, over 5TB of HD space, an SSD, etc. A very good PSU (where OEMs use trash). The motherboard has an over done VRM phase, and solid caps compared to the shit electrolytic ones Apple uses. Also, my stuff isn't all cramped together, and has superb airflow. The case is awesome to work in.
PICTURE LINK
Here's the Specs and cost:
$220 - I5 2500K
$129 - ASR P67 Pro3 Motherboard
$60 - G.Skill 8 GB DDR3 1600
$119 - GTX 460 OC
$89 - HAF 922
$20 - CM 212+
$75 - Corsair TX 650 V2
$99 - 80 GB SSD
$79x2 - 2 TB Samsing HD 5400RPM
$59 - 1 TB Samsung HD 7200 RPM
$20 - DVDRW
$89 - Win 7
Total: $1137
Show me a Mac with those specs, at a cheaper price, and you'll make a believer out of me.
Noise level: The case uses big 200mm / 120mm fans. Since they are big, they spin slow (~800 RPM) but still move a lot of air. I'd imagine it rivals a Mac in terms of noise.
Footprint: A Mac is somewhat smaller, but really, it's a tower, it's not like it takes up a lot of room, really.
intangibles like style, macs own their category: I like the HAF 922 look. Style is subjective, what you like I may not, and vice-versa. However, with building your PC, you get to pick your case. When you build a PC you can always choose a case you like, this doesn't happen with Apple (or all OEMs really, but you referred to self built PCs in your OP), you take what they give you and that's it.
I stand by my assertion, a properly built PC is way better and cheaper than a Mac.