Tony, most independent computer stores will custom make any kind of PC you wish. My son has not purchased a PC in 30 years - he built every one of the 20 or so he has owned. You can purchase all the components from a number of online stores, then it's just a matter of plugging them in and installing the software, which is pretty much self installing.
Gary
Most computer parts are not tested, so you need to keep in mind that about 10% of your ordered part will fail you, you will have to figure out what part failed you and send it back for replacement..
Also the combination of memmory, CPu, mainboard is critical when it comes to timing, you can not just use every CPU with every type of memmory on a mainboard.. this combination is what used to create many of the BSOD's.. and still hangs your PC..
In this time, its probably even cheeper to buy a Dell then build your own, Dell comes with great warranty and service, well worth the few extra dollars.
Building computers is more then just plugging all parts in.. Sure if you're lucky everything goes okay, but if you are not, then you are in trouble.