Self-made/Custom VS Branded Desktop Computers

As far as I have seen

Self-made/Custom Desktop - For those that can fix computer problems themselves and know about how to avoid overheating the computer in general.

Branded Desktop Computers - For total newbies that need the "support" provided by these companies.

Is it generally cheaper to get Self-made/Custom Desktops though?

I stay away from any HP or Compaq, just because I'm a bigot.  Anything else is fine though.