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.
This is how I play Nasus
I went for a tank build with ability power. With Nasus's Soul Eater when you are lvl 18 you get 20% life steal it makes him a great tank. With Warmog's Armor and Rod of Ages you get bonus health which means you can go in the 5000 in health if you do it right and if you do your fury of the sands you could be pushing 6000 health. I have been able to get 5700 health. With the combo of Health regen and armor at that lvl you will be making people rage when you ace their team. The down side to this is your damage is not very high but Siphoning Strike and Ability power helps that. Just remember Wither, Spirit Fire, Fury of the sands, Siphoning Strike, and then Exhaust when they are trying to get away.