Should I buy a 'gaming' PC or build one?

A good handful of us know buying a gaming PC would mean spending quite some money if we want a good experience at the very least. It’s kind of that situation where you hope your money is well spent.
Now, I remember years ago I bought components like a graphic card, a fairly good fan, and other crap with my brother in law and we built our own tower. The end result was actually pretty darn nice. It ran smooth and since our objective was a gaming setup, that’s what we got. I encountered a few problems some time after, but nothing too drastic (overheating and things of that sort).
If I remember right, we didn’t spend too much money on the items we needed to put it together. So my question is, would it be better buying a gaming PC or simply building one if you know what you’re doing. I’m guessing building one would be cheaper.