Anymore, you probably won't save money building your own computer, whether Mac or PC. I don't have the time, patience, or tech savy to do it, though I like the idea of custom making a computer and selecting the components.
The biggest problem seems to be with software, not hardware.
OS X 10.11.6
iMac 21.5", Mid 2011
2.8 GHz Intel Core i7, 24 GB
AMD Radeon HD 6770M
Using Apple computers since 1980