Have you done any Googles for such sites? There are plenty out there. Many from highly respected e-magazines and forums. Try it, and while you are at it, try Vivisimo and Alta Vista as well. Who knows, maybe you will learn something.
I don't think there's any question that a person with ordinary skills, like being able to read and follow instructions, being meticulous about their work, having some understanding of computers and how they work, and a reasonably normal set of tools can construct as very competitive computer. All of the necessary components are readily available both online and at local computer parts outlets. The biggest problem is deciding what parts to use as the selection is staggering.
The first issue is what kind of computer you want to build. That includes the purpose its to be used for, the Operating System to be employed and which type of processor will be used. The type of computer could include tower or small form factor or even portable (though a true notebook is probably out of the question as getting the chassis and mainboards is very difficult and expensive). Operating Systems include various flavors of Windows, Unix/Linux, and other exotics. Processors are extremely varied but the main catergories are Intel types (both Pentium 4 and Pentium mobile as well as Celeron and other older models), AMD, VIA Eden, etc. Lots and lots of choices. Best to work all that out before you even start to look at specific parts. Also a good idea to set yourself a budget, one that breaks the total cost down into how much you should spend for each major component as well as a slush fund for all the little odds and ends. and a time table. Once you have settled on a type, an OS and a processor, you should look into Graphics systems, the processors, the cards and the displays. After that, you can decide on the rest of the peripherals. But I repeat its a good idea to work out what you want before you start buying anything. Figure the whole thing out in detail. Then see how it works with your budget.
And yes, Ars is a good starting point. Certainly not the only one but a good start.