I guess building damage on nasus is worthless, you will have tons of damage because of ultNasus - has become a beast again.
I've started laning with nasus top and my god is he stupidly op against most champions. I've laned vs Vi/Riven/eslite/kennen/ryse/olaf/jax in most of my games. In every game I have won my lane.
Some were harder than most (olafs true damage early game was a bit of an issue) but most of them I could farm my lane and rarely if ever leave it. Took ghost +teleport took tank runes and masteries. Not only that I build almost pure tank items and used the iceborn gauntlets or w/e they are called as a good tanky dps item. (usual build is a sunfire legion gauntlets and then its something im lacking either a randiuns/thornmail or a frozen mallet etc.
In one game even got to 850+ damage on my q. With home guard boots + a teleport and sprint in one team fight at baron I came in and just ploughed through to their carry. It was disgusting.