Friend is rich. Runs his own business and makes ton of money.
He will probably buy new parts every 2 years if not yearly, just because he can.
He recently got into gaming and wants me to set up a "Gaming Station"
He already has a giant TV and all the consoles, just need the stuffs below:

Budget: Let's say $5000~10,000 USD
Needs Everything including Peripherals (monitors, keyboard, mice, headset, speakers)
I want a classy build with a triple monitor set up. 4K Please.
Rig will purely be used for gaming. Don't need crazy 8 cores if 4 will perform the same on games. (no need future proofing he will replace parts every couple of years)
Reliability is also a key factor. I don't want shit breaking and getting blamed for building a shitty rig. So perhaps a raid setup as well.
Please use reliable/trusted brands only.

Threw something together in a hurry, maybe something like this?
http://pcpartpicker.com/p/xZwJRB

I never tried using a custom loop, but I might look into it.

Given the nature of how computer parts are, there is zero reason to spend that much money ever - much less so if you're going to replace them every year. If he is going to replace his PC completely every year, he's probably going to end up selling his old one and that's going to be really hard if it costs 5000+ to begin with.

That being said, if thats what he really wants...

http://pcpartpicker.com/p/2x9YwP

Then add about $700-1000 for a custom water loop on everything.
Remove the bezel on the monitors and run them in surround mode.
Change the mouse/keyboard if you want to.
You can use a different case if you would like to, just make sure its big enough to accommodate everything. Don't forget about water pumps, reservoirs, and other parts that aren't listed. In fact, a custom case would probably be best.

How you set up the water loop will mainly determine how the fans inside the case are setup. You can put everything on water, chipset, ram, gpus, cpu, etc if you want to.

http://pcpartpicker.com/p/qdrssY

Will cost $1500 + more if throwing down a custom loop, though it's already over $12k.

go B.I.G. or go home