Basically this build is almost an exact copy of Ninjaken's build. Ninjaken is a very high elo (used to be 3rd spot in challenger) nocturne player and at first I thought he was crazy for building tirforce on noc. Then I tried it.

I'm not actually very high elo, only silver 1, but I have been playing nocturne for quite a while. While I'm not ninjaken, I can tell you how I play nocturne.

this is ****ing op
you should probably use this build most of the time
triforce helps a lot in fights and for ganking
phage procs, dayum

use other build if you're sucking or you're having a hard time ganking and you think you're gonna spend most of your time jungling and counter jungling

start machete 5 pots
get wriggles and boots asap
rush triforce (phage + zeal + sheen)
randuins
blade of the ruined king
GA if you're getting focused, warmogs if you're not
sell wriggles for bloodthirster, last whisper, or SotD (if u need to kill a carry really fast)

warding enemy jungle is good because you can counterjungle them easily, maybe even find and kill them

if you're against someone that likes to counterjungle like nunu or shyvana, ward your buffs so you and your teammates can corner them and beat the **** out of them when they try to **** up your jungle

sometimes if a teammate is playing like ****, just warding their lane can help them out more than you think

nocturne's ****ing op
people think his ganks are **** pre-6 but they're actually pretty damn good
lots of people think they can 1v1 you so beat the **** out of them
you're strongest mid game, right after you finish triforce, so kill people even more then
when you're against jarvan, take flash instead of exhaust or ghost
**** jarvan

when you play noc for a while, you'll get better and better at using his spell shield
don't burn it right when a fight/gank starts
wait until you know/think somebody is probably gonna use their hard cc on you and block that ****
it'll make champions like tf and lux cry
hue

Pros:
tons of damage
jungles really quickly
strong ganks that get really scary when you hit 6
pretty powerful throughout the whole game, doesn't drop off much
good at counterjungling
can stop hard cc
good at chasing
dat ult- amazing map presence once you hit 6
can kill squishies very fast

Cons:
impossible to escape from **** you can't spellshield or juke (jarvan ult)
not very useful when he's doing bad
pretty reliant on landing q during a gank
lots of champs can escape your fear
bad against tanky people
pretty squishy

if you've had success with this guide, feel free to message me the game stats and I'll put it on here