More or less I have nothing better to do and this is my first, and probably only build for quite a while, so try it, ignore it, hate on it, love it, up to you

Not gonna bother spending too much time here
Pros: Likely the biggest snowball jungler there is, and very strong counter jungle, fantastic ganks with ult
Cons: If shut down very squishy and hard to get back into a game, and if you dont nail your skill sequence, they'll just run away laughing at your ganks

Fairly simple, start wolves, get a leash on blue, go wraiths, golems, red, recall, begin ganking, once level 6 gank every time your ult is up

Runes are fairly standard, again this is for passing time so I wont go into detail, get the standard yellow armor, blue MR, and then the quints i recommend attack speed, with armor pen reds, these can be replaced with attack damage, more attack speed, or more armor pen, pick your poison

Masteries again are fairly basic, get some defense, get the runic affinity, and enjoy

Q is Nocturnes main damage and gives him his steroid that makes him the threat he is, if you miss hitting your Q, you're gonna have a bad time
W is Nocturnes spell shield with the convenient passive, level this once at level 2, and max it last
E is Nocturnes fear, its used mainly for the crowd control, as it scales off of AP, and nobody in their right mind will build AP Nocturne, max this after your Q for fear duration
R is obviously Nocturnes ultimate, and its what makes him such a great ganker, use this every time it is up, later in teamfights you should think twice about initiating with this, as it will leave you alone against their entire team, an effective way to use it late game is to initiate with your Q, and when you see the ADC separated or low health, use your ultimate to assassinate the carry, then depending on your health situation you can make a quick getaway while the enemy still has reduced vision, or just jump back into the fight

This is just a short basic build that I use on my Nocturne, feel free to tell me I'm bad or leave polite recommendations, depending on your mood, not trying to make the top builds here, just throwing it out there because I had nothing better to do.