Inventory and Evaluate first
I just got through rebuilding a machine to Adrian Kinglsey-Hughes' ZDNet November 2011 Skyvim: Elder Scrolls suggestions. (Mostly because my wife managed to fry the bios chip on the last system - heck it was 4 years old anyway)
Of course I usually assemble systems to what were high end specs 6 to 12 months ago, and whose components are now in a sweet spot for price and lack of bugginess. What I ran into was the new motherboard no longer had capability for IDE devices (DVD/CD read write), only SATA and USB, wich required a second order for compatible drives.