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?

Brand computers have a good design usually. Dell for instance has clamshell cases and a separate path for the heat from cpu to flow. Compaq has slide and lock for hard drives, 1 screw to open the case. If you were to buy a cheap custom case you will most likely get crap.