Since you already have a budget which is under $1000, and you're gonna use your computer for gaming...
Figure out whether you'd want AMD or Intel and if your going to overclock your system.
Research for components/parts and their price then write or type them, change anything to fit the budget.
Notes: For CPU and Motherboard just check their socket types to see if they're compatible. for GPU, check motherboard if they have a PCI slot, mainly they all have one except for m-ITX boards.. PSU for one GPU 650w-700w is enough, two GPU's 850w-1000w depending on the card. RAM, 8Gb is enough, anything more is of preference. SSD, if you want loading times, copy-paste work to do faster, and windows to boot faster.
Found this at newegg,
AMD 2nd Gen FX-8320 build for $514.99
you'd have around 400-500 dollars to buy a card or two!!! :D
Try a
7870 card or
7970 or a
GTX 680.. you'll get awesome fps, or overkill depending on you monitor.
Thanks,