Hi Guys,
Here is my Guide for my Way to play Nasus! You must know, I cant write a lot because I cannot speak English well, I am German :D This is my Build for Nasus and I play it very often in Matches and it works pretty good. I think, I neednt say a lot about the runes and Masteries, I have defense at the beginning and at the End +35 attack damage with the runes.
Take Flash and Exhaust as summoner Spells, because with flash you can run away and your wither cost a lot of mana and I still need it soo often.

I always start with Dorans Shield, because Its a good Start Item with some life and Regeneration. I take the Ninja Tabi because they are cheap and at the beginnign you need more armor than magic resist. After that I take Aegis of teh Legion because it gives a good Buff for teamfights and there are not much Items which give life, armor and magic resist. Then i pick Sheen and Build it into Trinity Force. This is a very good allrounder Item!
Now I take Hexdrinker for more Magic resist. Then, take The Bloodthirster, because of self heal. I take Infinity Edge at the end, because you make crit with siphoning strike. You also can pick a second Bloodthirster, then the enemys are your heal :D

Your Siphoning Strike is the most important thing, because you must stack it (with last hits on vassals) and with more damage for your ss and better cooldowns you can do it better. Your Wither is there for slow enemies, but you dont need it on lvl 5, thats a big waste. Ghost fire is there for hold enemies back. When you are sololane against 2 champions, skill Ghost fire because they keep you on distance for stack.

The most important thing is your SIPHONING STRIKE, make as much last hits as you can! When you do it well, you have over 400 stacks at the end (!) With so much stacks and so much damage you make over 1000 dmg :-)

Conclusion: Nasus is a very good AD-Champion, but I think only in the end game. With this Build, I won lots of matches and I changed defeats in Victories :-) I hope you understand my Guide and i wish you a lot of Fun with Nasus and His New Skin ( With patch v1.0.0.116).

Tell me questions and Suggestions, make a comment :-)