Nasus is pretty awesome, and I'm glad to see another player enters the fray by playing him!
I normally run this build. I grab a Philo Stone, and HoG. After that, I go into either Sheen or Phage, then into Trinity Force. After that, I generally just build a Frozen Heart or FoN, then whatever I need to counter the other team. Of course, if I'm losing, I'll grab whatever I need to survive in lane.
If you're winning lane, never be afraid to trade with the other person. Once you have Sheen, you should out trade nearly every top laner. Throw W on them, lead them with E, and smack them with a Q while they're in the circle. If you want to do more, just keep hitting them. Most people don't want to fight with you if you're powerful. If they do, pop ult, and FOR SURE they won't want to fight you then.
I personally run ArPen reds, Flat armor yellows, Scaling MR blues, and Movespeed quints. I feel like this provides a good basis for late game, without making you too vulnerable early. You can switch blues to flat MR if you're up against a Cho'Gath/Vladimir.
As much as I love Nasus, I don't recommend him for most lanes. He requires farm, so people who put out much pressure early without needing to auto attack will hurt you greatly. Some of these are Darius, Vlad, and Jax.