The first thing you should think about is the processor (CPU).
Why? Because it'll dictate what motherboard you get, as both the CPU and motherboard need to be compatible. Don't worry, I'll suggest a good motherboard soon.
When you're buying parts for a new gaming PC, you generally want to get the latest generation CPU. While most games aren't super CPU-intensive, it's a good idea to get a powerful CPU that'll last you a long time if your goal is to keep this gaming PC for several years. With that in mind, avoid getting a Core i3.
The Intel Core i5 6600 is a great, mid-to-high end CPU that'll serve your gaming needs now and for years to come. It's part of Intel's latest line of CPU that are available to buy.
Its "socket" type is LGA 1151, which means it'll fit in motherboards that support the 1151 socket.
Price: $215
A CPU cooler.
The Core i5 6600 CPU may or may not come with a cooler. Either way, you're better off getting a good cooler like the CoolerMaster Hyper 212 Evo.
Price: $35
You don't need to go crazy with motherboards.
The MSI H110M is a great, inexpensive motherboard that'll fit the Intel Core i5 6600 CPU.
There are bigger and more expensive motherboards out there, but they come with a bunch of superfluous features that don't make a perceivable difference in how well your computer and games run.
Price: $45
Next up, the RAM.
Both the i5 6600 CPU and the MSI motherboard support the latest generation of RAM (random access memory), called "DDR4."
The MSI motherboard supports up to two "sticks" of RAM, and I'd suggest getting a minimum of 16GB.
With that in mind, two sticks of 8GB Corsair Vengeance LPX RAM will do the trick nicely.
Price: $94
And now, the fun part. The graphics card.
The graphics card is the most expensive part of your gaming PC build.
You're better off splurging on a powerful, expensive graphics card that will play games at high graphics settings (in 1080p) for several years rather than going down the economical route and upgrading several times over the years.
With that in mind, the Nvidia GTX 1070 and GTX 1080 graphics cards should be your weapons of choice, depending on your budget.
You can get a GTX 1070 for $400, and a GTX 1080 for $630. That's a $230 difference, hence why it's up to you and your budget.
You'd be fine with either, but the GTX 1080 will play games beautifully and smoothly for a little longer than the GTX 1070.
Price: GTX 1070 for $400.
It's worth getting a decent power supply.
The power supply's one job is to pump electricity at the consistent rate your parts need. It might not make games look or play better, but it's not something you want to be cheap about. A bad, low-quality power supply could fry your parts.
This power supply from Corsair has a rating of 80+ Bronze, which isn't the highest rating, but it'll be perfectly sufficient and stable for your parts.
Price: $70
A nice home for all your parts: the case.
The case design and cost is totally up to you.
Considering the size of the motherboard I suggested (microATX), I wouldn't suggest getting anything bigger than a mid-sized tower. Otherwise, the case will be overly large with a bunch of empty space inside.
The one pictured above is the NZXT S340 mid-tower, and it goes for $70.
A few fans to keep things cool.
Check the specs of the case you're looking to buy to see if it comes with any fans, as well as how many fan ports it has.
Cases usually come with at least one fan for the heat exhaust around the back. If it does include a fan, it should be fine.
If the case has a few more ports, especially at the top for extra heat exhaust and on the front for cool air intake, get fans for those ports. Make sure to note what size fan the case's ports support. Most fan ports and fans are either 120 or 140mm.
Some fans come with LEDs, which could make gaming PCs with windows look pretty sweet. You can even add LED lights into the mix to make something crazy, like the "all-white build" above.
Optional: a WiFi card.
Unless you have Ethernet ports where your gaming PC will dominate, you'll need a WiFi card to connect it to the internet.
Some motherboards come with built-in WiFi connectivity, but they're not known to be very good, so getting a separate card is a better way to go.
I've been using this $60 WiFi card from Asus on my own gaming PC with no problems or issues to speak of. It's an AC1300 dual-band WiFi card, in case you're wondering, and it comes with an antenna extender cable, too.
Price: $60
And don't forget Windows 10.
If you don't already have a Windows 10 product key, you're going to have to buy it.
You can get one from Microsoft for $120.
Building your own gaming PC can get pricey, but you'll have fun assembling it, and you'll get great satisfaction from using a computer you built yourself.
The total cost of the parts with the Nvidia GTX 1070 graphics card is $929. Add $120 to that if you need to buy Windows 10.
For the same parts, but with the Nvidia GTX 1080 graphics card, the total cost is $1,159. Add $120 to that if you need to buy Windows 10.
It's a high price, but you get a quality gaming rig that'll give you years of fun and satisfaction. You can also upgrade some of the parts over the years should you need to, like the RAM and the graphics card.