ATM i'll try those build, but Nasus is very strong when you reach a point that AP and you're Q are so high that you'll just 2 shots the AD or AP carry.

Those runes could be changed a little if you're a tanky AP or hard poke AP like lux, you should ajust some of them.

i prefer those masteries for the damage, CDR, scaling ap and the mana regen.

Try the best to reach carries, AP or AD, and just smash them !

you must freeze the better you can, to farm your Q, and let the jungler come for an easy gank with your Z.
don't forget that your E will push hard.