The perfect Nasus runes etc. (400 stacks at 20 or your money back)
Okay so I played some games of Nasus on another account and I've found the secret sauce to Nasus success.
Primary tree: Resolve
Keystone: Grasp Then: Demolish/Boneplating Then: Conditioning Then: Overgrowth (Any of the last 3 can be good)
Secondary tree: Inspiration (Doubles down on the hp, you don't need damage runes with all the staks u gon' get)
Biscuit Delivery (Helps survive laning phase, you can lose trades and heal. If you stomp the lane you can also use them to get more mana to stack with)
THEN THE GENIUS 300IQ RUNE:
Approach Velocity
When you wither someone, you can just run them down. Phase rush is a bit faster but with the Phase rush keystone in the Sorcery tree you get less hp and you never need more than the speed of approach velocity (With phase rush you're often outrunning your opponent where approach velocity would have done the same job) and phase rush makes you play a minigame to activate whereas with approach velocity you always get the movement speed buff exactly when you need it.
General advice, let your laner push the first wave, and against champions like Jayce, completely concede the lane for 10 minutes and stack under turret. Never E the wave, because if you push out early they can just freeze it and deny you all cs or spank you for trying to get any. If you shove the lane you genuinely have to do your best to hard shove it until you almost die and then TP back to your turret, anticipating the wave coming back to you.
Items:
Fist buy: 
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Boots:
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First back:
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and:
First item is probably one of these:
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Full Build Something like:

If they can kill you, you go Sterak's to survive. If they cannot kill you, you go Warmogs to heal back up after the fight. I'd never go for both.
If you're stomping and want to 1v5 turret dive:
If you're getting
compounded:

to Draintank even harder as well as hitting for much more.