Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
I left the Mastery tree blank because this is simply the item, skill and rune build I use to be most effective at laning and tanking. What you put your Masteries in is up to you. I start with Physical resistance because most of the damage you receive will be physical early on because no ones abilities are quite strong yet. If there are Mages present in the game ( Which the chances are high) then you'll want to get Force of Nature before Randuins omen to hold out against Mages. I chose to go all mana regen in my runes because Nasus's abilities are to good for Laning to pass up spaming them. The Spirit fire alone will take out most of a minion wave at level four, so get that up as fast as possible and focus on getting last hits with Siphon Strike, this is where alot of your endgame damage will come from. Wither will be saved for last to level up because the slow is quite good even at level one, good enough that if you catch a DPS champion with it, your DPS should catch him with no problem. I chose Dorans Shield as my starting item for the health boost and the extra health regen early on. I could not recall which skills were able to be leveled up at which so if it's inaccurate, I do apologize. DO leave feedback on this build. Clarity was Chosen as a summoner spell because Nasus with no mana is pretty useless. Exhaust is best used after wither has worn off, to make the slow that much longer.