Posting a few things here in case I don't have time to answer them before this build but I've offered my help in the physical part of the process. I'll do what I can for shopping around for components but here's my estimate of needed info.
1. Price range? I think ~$1200 will build a pretty damn solid gaming rig if we're not worrying about adding a monitor, mouse, and keyboard into that.
2. Multi-monitor or single monitor setup? Are we including monitor/mouse/keyboard in cost or is he for sure keeping the old stuff? If keeping old stuff, what's max res on monitor? No point in buying a GTX Titan for a 23" monitor that's only running at 1920x1080 right? FPS will be negligible difference for the price if all other components are solid? I think a GTX 760 would do nicely.
3. 16gb of ram should be plenty. To my knowledge, few to no games utilize anywhere near that, let alone 32gb.
4. Case/overall form factor. How old is this kid? Does he like shiny flashy LEDs? Simple minimalist efficiency that won't take up as much space? Full tower ATX that may have lots of fans, runs noisy, and ends up with lots of empty space inside because you're not running a triple crossfire setup? Or micro ATX for a single vid card, mini tower/micro ATX case that still looks cool but doesn't take up anywhere near as much space and runs cooler and quieter? Personally I think you can't go wrong with a Silverstone Temjin TJ08-E, but there's flashier cases out there he may like as well.
5. SSD/HD combo. I think a 128gb SSD for the OS + COD/BF/LoL/WoW will be plenty, with a 1TB - 2TB normal HD for movies, music, other games, pr0n, whatever. Max I would go for a budget - medium range build would be 256gb.
6. CPU/Mobo- probably require the most research out of all other components besides case. No need for a top of the line i7, one of the quad core i5s will be more than sufficient, but overclocking may or may not come into play in the future - I'm going to guess no for now, but if your kid's talking about water cooling and hardcore gaming we may want to buy something future proof he can fuck with later once he gets so inclined. Overclock.net has a ridiculous amount of info, tips, tutorials, tweaks, even subforums dedicated to liquid nitrogen builds.
BARF, if you guys can line up the components for the price range he wants I'll be happy to build it for the small price of getting to borrow that Sumo for a day or three

cold weather be damned I'm gonna want to ride after finals are over this week.