The one thing your going to spend half of your money on is the water cooling.
Make sure you spend more then 1-3k on it, cause if you don't you could end up springing a leak or worse.
After getting the right water cooling buy a good PSU, I can't stand how many people go buy a cheap one and wonder why it short out their whole pc.
After you got those 2 vital things down spend the rest on a good GPU, CPU and motherboard.
If don't know much about it then go find a computer that is already put together.
Aerodrifting Systems has really good gaming computer from a range. I would try with those if you are not 100% sure.
If you had the extra money I would go with
Liquid Cooled Intel Core i7 3970X GeForce GTX 690 Quad SLI Gaming Computer PC | eBay