I play Nasus for so long. Now I am level 30, I play him as a jungler.
I can explain this choice for many reason :
- During early game, Nasus can't hit correctly. He doesn't have damages to farm correctly. He need his SPIRIT FIRE to get gold.
- When he is solo, he is so armorless that he must stay under tower and, if he does it, the tower hits the creeps he wanted.
- When he is with a DPS to kill heros, he can't farm his SIPHONING STRIKE. And when he is with a tank, he can't make any kill.
I can say it, he is useless in early.

In jungle, he can take his time for farming. He can buff his SIPHONING STRIKE and his SPIRIT FIRE enables he quick jungle. His level is equal the midder. And his WITHER makes him a perfect ganker.

I choice those runes to take advantage of his life stealing. In red, I don't take armor penetration because it's useless with his SPIRIT FIRE. You must take armor because of his weakness. And the movement speed is just to be quick for jungle and for ganking.

I have tried many groups of masteries. But this is the only one which allows Nasus to take blue buff without a lot of damage. Moreover, I need exhaust to be sure the ennemy can't leave, and smite must be taken for jungle. So Utility can't be chosen.

I begin my jungle with a cloth armor and five health potion like a normal jungler. The Madred's Bloodrazor is to farm easily, the Ninja Tabi to escape more attacks and Trinity Force to upgrade his SIPHONING STRIKE. The other items depend the ennemy team composition. A carry AD will be contered with a Thornmail and an Atma's Impaler is a good choice to get more damages. But don't forget magic resist with a Banshee, a Force of Nature or a Quicksilver Sash.

I begin the jungle with FIRE SPIRIT to make the blue buff low armor and with my attack speed I kill him mid life. I become level 2 when I kill one wolf and I can farm my SIPHONING STRIKE. The SPIRIT FIRE allows me to make jungle so quick the mid lane is same level than me. A SIPHONING STRIKE is useless when it's not farmed. So I just choice once during my first levels. The WITHER is a ganking spell. So you must take it level 3 or 4. It depends the moment I want to gank.

The smite is already the best choice for jungling, and exhaust is the best one to kill with Nasus. It allows to slow 2 times, to slow attack speed and to fall damages. I can spell the both together or just one, and 5 seconds later, the other, as I wish.