Installing windows 8.1 on new gaming pc

[unslaved]

I'm about to build a gaming pc but I'm in need of windows, trying to find the cheapest one and found one on g2a.com but they only sell the key
I'm wondering how can I get the windows CD or bootable USB flash drive with windows in it.
Have any of you had any experience with this page or buying windows from them?

 

[EliteMKD]

you can make bootable usb with this program http://rufus.akeo.ie/ you will need at least 4GB flash drive.

 

[KyleADunn]

This OEM version from Newegg should do the trick! $99, plus like $2 shipping. This is the basic windows 8.1, so it won't have Media center like 8.1 Pro. But if you don't use media center, it's no problem

http://www.newegg.com/Product/Product.aspx?Item=N82E16832416776&cm_re=windows_8.1-_-32-416-776-_-Product