These are the great sites, the link above, if you are considering building your own PC from the scratch. You can find any CP components with the reasonable prices. Especially the pricewatch is the best tool to checkout what is the current market price of each parts. Before deciding to purchase any component, you have to make sure that each part is compatible with the motherboard.
Customizing your own CP is a great thing to invest; first you will be able to get the very scalable machine you want if you do not really care much about money. So make sure that you are purchasing a motherboard that is good enough to handle whenever you need to upgrade your CPU, Memory and Video card. These are the three big CP components when they consider upgrade the System unit. Second thing about building your own PC is, you will be able to replace any damaged part by your own, and replacing them with the compatible one or even the better one. Third thing, it is the great thing to learn about PC world, you will understand very detail of computer. And last of all, it would be your pride to have one own that you customize it yourself, so that you can brag yourself to your friends or family with the best gaming machine ever you have had with the reasonable price. Even though it is very great, you have to limited yourself how much you want to spend and what kind of work are you going to deal with.