I experimented with having my vendor build systems for me, figuring it would save me (at the time) 2-4 hours. The thing came in with a rattle when the fans ran because one of those blanks which cover the CD bays vibrated in it. I started it up and got immediate errors. I essentially had to half tear it apart and rebuild it, then reinstall Windows
+1
I did the same thing many years ago. Trying to save time. But when they started arriving with fans not screwed down or screws stripped, motherboard standoffs loose, missing or held down with the wrong screws, ram not seated, wires not connected properly, even a few cases where the CPU was not correctly attached etc, etc.