I am a 14 year old who needed a better computer, as my two year old laptop is not adequate anymore for the games I play. The main uses of this computer are to play battlefield 4, far cry, and FSX at 60 FPS maxed out. I saved for a year and a half and shoveled TONS of snow off people's driveways to make money for this build, so please be gentle. Here is a more in depth description of why I chose each part.
CPU: I chose the 4570 because it was a bargain at microcenter, and I don't intend to overclock, so I don't need a 4670k or additional cooling. Also, I got a particularly good bin of the 4570. Most of them only boost with 1 or 2 cores up to 3.5 or 3.6GHz, with the others staying at 3.3 or 3.4Ghz. Mine, however, stays balanced at 3.55GHz across all cores.
Motherboard: It was cheap at microcenter bundled with my CPU, it's from a reliable brand, and it allows me to add another 770 in SLI later, so over all, I'm pretty satisfied with it. Also, from what I've heard, it's fairly good for overclocking, so if I get an unlocked CPU down the road, I should be able to achieve a good overclock.
RAM: It runs at the speed and timing that I wanted, is reasonably priced, and matches my motherboard, so it was a no-brainer.
SSD: This was something I chose to add on the last minute, and hold off on the new monitor until later. I am happy I chose to have an SSD, as my system boots amazingly fast.
HDD: It's cheap, reliable, and I don't need any more than 1TB, so it's a good fit.
GPU: I was initially going to go with a 280x, but the price skyrocketed (I built this PC in January), so I went with the 770. I chose PNY because they are one of the few companies that still offers lifetime warranties on their high-end graphics cards. I chose the 4GB model because I might upgrade to 1440p and SLI a second card in the future, and 2GB is not enough for demanding games like BF4 at 1440p. Also, the cooling is pretty good, but it does make a fair bit of noise, especially summer when it gets hot and muggy here in Boston, and the card runs hotter. I gave it a bit of an overclock just for a slight performance boost.
Case: It's roomy, offers pretty good cable management, and is pretty cheap. Note that I don't have any additional fans because I don't need them. I have the PC right in front of my air conditioner, so plenty of cold air blows in through the back.
PSU: I was originally going to go with a CX 600M, but this was a bargain at microcenter, so I chose it. For a PSU, it's massive, but it's fully modular, and very high quality. That said, I intend to replace it with an 850w Supernova G2 when I get enough cash, so I can add another 770.
Optical Drive: I need one to install older games which I have on CDs. I just chose the cheapest one I could find, and it works for what I need it for.
WiFi card: I initially was using Ethernet through a remote router, because their are no Ethernet ports in the room where I have the PC, but my remote router failed, so I figured it was worth the 15 bucks. I am surprised by how fast it is. It makes me realize that the one in my laptop is a piece of crap. I can stream 2 1080p videos at once with this guy.
OS: Windows 8.1 really isn't as bad as people say. If you don't like the new UI, just install classic shell, activate administrator account, and BAM! it's basically Windows 7.
Monitor: I was lucky enough to get this monitor on a one day overlap period between a promo code and rebate on Newegg, so I got it for dirt cheap.
I also have a fairly nice joystick (Saitek X52 with separate stick and throttle) for FSX and jets in BF4. I have had this for 2 years or so, which is why you don't see a price for it.
Overall performance: It runs everything maxed out at 1080p. BF4 usually runs about 80FPS, occaisionally dropping to 70 or 60 on bigger maps. It does sometimes drop below 60, but this is very rare, and it never goes below 50. FSX runs like a dream, even heavily modded. I simply set target frame rate to 60FPS, turn V-Sync on, and forget about it. Far Cry 3 is the most intensive game I run, but it does run smoothly, even in intense scenes such as raiding enemy bases, or blowing stuff up. I generally get 50-70FPS with everything on ultra. It does generally make the GPU run hotter than the other games I play, but only by a few degrees.