I do this when I'm bored, go to my favourite supplier's website and select stupidly specced components to get the most humongously over the top desktop. It is getting increasingly difficult to get a desktop over $10,000 without being completely ridiculous. I used to do a lot of builds for friends and relatives, but now I generally recommend that they buy an off the shelf if they are looking to save cash. I will do upgrades and specials for people but only when the realize that they aren't going to save money but they will gain reliability. I actually make more money from fixing off the shelf laptops etc that have had a component failure.
About 6 years ago I was in the position of buying the fully specced machine that I wanted. I cost me an arm and a leg, and I got a Case that had space for 15 drives, and could also be used as a backup nuclear shelter, nVidia 7300GT (this was an HTPC setup so no huge graphics needed), modular 850W PSU, 1TB in 250GB drives, Nvidia 4GB DDR2, Quad core Q6600 running at 2.4 GHz, with a dual tuner. Over the years I have changed the drives, first to 2TB in 500GB drives, then to 4TB in 500GB drives and then to 8 TB in 1TB drives, and the addition of an SSD as a boot drive, upgraded from XP MCE to Windows 7 Ultimate, everything else has pretty much stayed the same. This machine has been on 24/7 for the last 6 years, the investment in quality components was worth it, I'm sure with consumer grade Gateway/HP/lenovo/Whatever I would have been on my 3rd PC by now. At the time this rig coast about 150% what I' would have paid for an off the shelf close equivalent. So no money saved on the build but money saved over 6+ years of use. Even now the rig is more than up to its task and excluding component failure I see it lasting for at least another couple of years before I have to bite the bullet once again.