Hi there,
My advice, dont get a pre built. Start googling-reading various here and there articles and watch some youtube videos on how-to-build a gaming PC to get familiar with all the basic connections. After that it really depends on the selection of components and your ability to understand them- basically the connections are the same..
However if you are unsure on how to do all these why dont you ask someone, a friend maybe that has built his own rig or pay someone (that its his job) to build your PC. As far as the components 1000$ will get you a decent gaming PC. Personally I have built 4 1000-2000$ desktops for me and a friend of mine only by doing these stuff and its really rewarding. I remember when we got to my place and built 2 identical gaming PCs some years ago that we would use to play online fps games.. It was really fun and the result was perfect! We made sure that all parts were ok with each other and never had problems, except for a case that it proved to be a faulty component that was replaced the same day I realized it was bad.
The only downfall is that you need time, if you cant afford the time, then keep asking. I'm sure someone will suggest you a decent pre-build. Make sure it has a good graphics card tough. Thats what you need for games. A Radeon 7970 or Nvidia 670 or 680 or 770 GTX for example will give you next gen games at 1080p high-ultra settings.
Cheers