I am curious if those that build their own, upgrading a piece at a time, keep up with a running tab and compare that to buying a new one when a total upgrade time comes along. The price difference can not be that great I would not think.
For quite a while in recent years it was no more economical to build than to buy. Recently, I was checking prices for a friend, and found that I could save him quite a bit by building as I was surprised at just how much higher prices are now than in previous years.
Even if the cost is the same building has a number of advantages:
1. Better parts for comparable price
2. Design specific for user's needs
3. Better warranties - usually a year on bought units, 3yrs on mobos and psu, 3 to 5 years on video cards, 3 to 5 years on drives.
4. Much better features available - especially for connections.
5. Not locked into proprietary bios
6. Operating system not tied to specific machine.
7. Upgrading much easier.
I do my upgrades by watching for extreme bargains by subscribing to newsletters and ads from retailers. I get a lot of software free and hardware at great prices. My system gets upgraded constantly at very low prices. I then use the old parts for another system that I can sell or give to a family member or friend.
Almost forgot the biggest reason to build: Self-satisfaction and feeling of accomplishment.