Once Nasus gets to the point where you can't zone him anymore, just leave lane and help your team, no point in sitting in lane with him watching him stack. Keep an eye on botlane, you can 
right in front of him and he can't do anything about it because his kit has no interrupts. He usually won't follow you if you roam early because then he can't farm his Q, and after you help your team win enough 5v4 fights and dragons they will eventually rotate top and kill him for you.
Contrary to popular belief, leaving Nasus alone in lane (don't straight-up abandon the lane) does not result in an automatic GG, this is a myth propagated by Nasus mains like me because we hate it when our team screams at us for making them fight 4v5 early in the game so we would rather our lane opponent farms with us so we can keep an eye on him. Trust me when I say that a Nasus that was allowed to farm to 600 stacks by 25 minutes does absolutely nothing if the enemy midlaner and ADC is 12/0 because top lane kept helping them win teamfights. Do you know what the actual winrate for a full-time 4v5 game is? It drops from 50% to 15%, and that's exactly what Nasus does to his team for most of the game.
Every single time i'm matched against a plat or diamond in my normals games and they aren't playing a champion that can outright kill me before my first back, guess what they do? They don't try to outfarm me or try to dive me in my own wave, they shove me to my turret then either go into my jungle and kill my jungler, walk towards mid and kill my midlaner, or teleport bottom and get their ADC fed. And they don't immediately come back to lane either, Q stacks be damned they couldn't care less about my personal minigame. They will often stay in the lane they ganked for several minutes to make sure that the turret falls, because once the other lanes have taken down the turrets they will naturally start sieging the only outer turret still standing AKA Nasus lane. These players don't try dealing with Nasus 1v1 because they don't have to, if the rest of his team loses early game then 3 people are going to start sieging his lane before he has enough stacks to become a threat and now he can no longer safely stack.
& sometimes I'm stuck with it.
can really hurt him.
My top champions I want to be good @ are 
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Do Runes play a major factor even if enemy Nasus has Only AP power & Attack damage yet has No armor or Flat Magic Resit.
