I don't see any disadvantages to building your own. It's cheaper, you can get exactly what you want, and most all components carry a long term manufacturer's warranty in case anything goes wrong.
I've been building my own going on 19 years now. I got my first computer from my father in law. It was an old 33Mhz Intel system. First thing I did was to tear it apart to see how it worked. It's been down hill ever since.
if i should wait for usb 3.0, sata, 3.0, ddr4, and PCI Express 3.0