Wait......you want US to design your computer for you? What's the point of building it yourself then? It's just like buying one a prebuilt one, except you have to put it together yourself, and should something go wrong, troubleshoot and pull the part yourself.
If you don't feel comfortable designing a PC yourself, go to your local computer shop. They will have several premade configs, and they you can just buy the parts from them and assemble it, or they can build it for you (you often get a warranty on the system as whole this way, and it's usually a fairly small charge compared to the cost of the parts)
If you want to start piecing your rig together.......some things before you start:
Building a PC is a lot like getting a pet: It's a lot of fun, and fairly rewarding, but it's also lot more work and responsibility than most people realize going in. YOU are responsible for taking care of this thing, and while you get warranties on all the parts (often for 3-5 years or more), and you can find forums to help you troubleshoot, there is no one you can take it to and just say: "This doesn't work. Figure it out and fix it". At least not for free anyway. You will have to install everything, including Windows itself. You will also have to configure all the parts and tune it. This will be mostly done automatically the first time you boot, but there are some minor things like fan settings you will tweak as you go along. I'm not trying to discourage you here, but if tweaking PCs isn't your idea of a very fun time, you may want to reconsider doing a homebuild, at least for your main machine. If this is a secondary computer intended solely for use as toy (ie, 00ber game console or HTPC), disregard this paragraph. Those should ALWAYS be homebuilt.
If you wanna do it, here are some tips:
-Pick your motherboard and case last. Once you pick one, you are limited to what they can support. You can find a case and mobo to accommodate pretty much any configuration, so pick what you need first, then find a board and case that will do the job.
-Don't skimp on the power supply. Seriously, DON'T! A cheapo one will cause no end to your headaches, and to small of one (even if it's built like a tank) will limit future upgrades
-Quad cores are good for video editing, audio production, e-p3/\/i5, and not much else. If you just want to game, consider putting that quad-core money into a higher-binned dual core, or something else entirely
-Why do you need so much HDD space? What do you plan to put there?
-Why a sound card? What do you need it for? What are your speakers? If they are PC speaker kit, don't bother. Use the onboard audio, you'll never notice the difference anyway.
-Spend a lot on the case. It's worth it. Things like a removable mobo tray, cable management holes, external storage areas, extra fan mounting points, removable drive cages and the like may seem a little excessive, but once you get used to any of them you'll find you never want to part with them.
-Stock GPU cooler is ok if it's 2 slot, not so great if it's single slot. Stock CPU cooler is never ok, nor is the thermal paste that comes with any CPU cooler
.....wow.....that was long winded. Sorry for the text wall.