If you aren't sure then don't do it. Grab a AIO and be happy as watercooling isn't just a case of throwing it on and leaving it, they require maintenance usually every 6 months for it to stay at optimum performance and cost a lot more for honestly, not that much of an improvement unless you go really big with multiple rads and pumps etc.
EDIT: not to sound like a buzzkill but it isn't the simplest of things to do, and anyway, a custom loop will cost a bit more than $200 when you factor in all of the hardware you have to get, especially as fittings aren't cheap. Which is why honestly unless you 110% know what you are doing then i wouldn't recommend it.

What Zayev said.

If you want to buy a closed loop AIO, there are some great options.

240mm:
Corsair H100i/GT/X
Corsair H105
EK Predator (slightly more expensive)
Fractal Design Kelvin S24

280mm:
Corsair H110i/GT/X
NZXT Kraken X61

360mm:
Fractal Desin Kelvin S36 (cheaper than some of the smaller rad size ones)

I would personally get the Kelvin S36 if your case can fit it, or the EK Predator if you can afford it. If not, then pick your poison between the other ones listed.

What case do you have?

_Skittle wrote What Zayev said.

If you want to buy a closed loop AIO, there are some great options.
360mm:
Fractal Desin Kelvin S36 (cheaper than some of the smaller rad size ones)

Unfortunately, the Kelvin S36 isn't for sale in USA for some reason that I do not know of.

Zayev wrote

_Skittle wrote What Zayev said.

If you want to buy a closed loop AIO, there are some great options.
360mm:
Fractal Desin Kelvin S36 (cheaper than some of the smaller rad size ones)

Unfortunately, the Kelvin S36 isn't for sale in USA for some reason that I do not know of.

I remember at launch they weren't released for sale in the USA due to a huge lawsuit pertaining to watercooling, surprised that it is still going on lol.