MY CHALLENGE FOR YOU IS, GO TO ANY TOP RETAILER (pc world, currys, dixon etc) get a specification of a pc you like and try and build to that exact specification.one major difference is the massive price slash. EXACT SPECS, MAYBE EVEN BETTER DESIGN AND WAY CHAEPER.
Benefits of building a new PC
The most distinguishing advantage to building a computer from scratch is the selection of parts. Most computer systems come pre-built with the specifications and components already selected for you. This often can lead the user to have to sacrifice certain features that they may not want to give up. By building a computer from components, the user is able to choose the parts that best match the computer system they desire. Some vendors do allow you to customize a computer system, but you are still limited to their selection of parts.
Another thing that users may not be aware of with pre-built systems is that two of the exact same model computer can actually have very different parts. The reason for this has to do with suppliers, parts available at the time the system was built and just pure luck. For example, Dell might switch between multiple suppliers of memory because one is less expensive then the other. Buying all the parts on your own guarantees what parts you will get in your PC.
Customization and Custom "Balancing": You build exactly the machine you want; no more, no less. This is an advantage you can only get by designing and building your own machine from parts you select--you cannot get this by buying a machine (unless you're extraordinarily lucky!) Part of this flexibility is being able to balance the system precisely as you desire. If you need a very powerful video card but not a lot of memory, you can get it. If you need 200 GB of hard disk space but only a so-so processor, you can get that too. In contrast, it's much more difficult to get pre-built PCs that are very "high-end" in one area but "middle-of-the-road" in others.
Quality: Most home-built PCs use higher-quality components than those used by companies selling pre-made PCs. The most common reason for this is that homebuilders care more about the longevity and quality of their systems than big companies do; that's just common sense. (Although high quality does require that you pay attention when shopping for components, and be willing to shell out a few extra bucks!)
Upgradability and Expandability: Building your own PC makes it relatively easy to upgrade or expand. Since you know what is in the box, you know most of what you need to upgrade it. In addition, if you plan ahead for upgradeability you can buy components that will facilitate this. Finally, home-built PCs use industry-standard components, avoiding the pitfalls of proprietary designs.
Easier "Non-Standard" Operating System Use: Most regular PCs are designed under the assumption that they will run the latest Microsoft consumer operating system. They are usually only tested on that operating system. If you plan to go with Linux, or BeOS, or something else "out of the ordinary", being able to pick your own components can be very helpful. For example, most retail PCs are equipped with Winmodems, which won't work in a Linux environment. (Also, most technical support people at big computer companies have no clue about anything other than consumer-grade Windows installs.)