For runes, I normally go armor pen reds, life steal quints, armor yellows, and scaling mresist blues. Masteries...well you can do one of two things: 9/21/0 OR 9/0/21. Going more defensive masteries if your team doesn't have a real tank is great while the utility of extra lifesteal (23% lifesteal and a bonus 3% spellvamp because why not at lvl 1 is awesome) possibility of 10% CDR from masteries, bonus starting gold for wards/potions and extra gold per 10 can turn an already highly successful sustaining champion into a farming machine. Disregard going B, farm under tower and make them waste time to gank you.
Good items to put in are Last Whisper as a sole pure damage item, IBG or triforce, locket, and if you're feeling trolly there is nothing like an Ohmwrecker to push down towers with plus the early philo stone helps sustain a lane where you *have* to farm under tower. --- You shall henceforth be known as, The Mover of the Wind, Breath of Air, The Lightning Zephyr. As dubbed by the Evil Dwarf atop the Wall
You have two priorities in the laning phase. 1) counterbuild your opponent 2) get CDR for Q stacking So basically Glacial shroud against AD, Visage against AP.
Since you get HP from your ult and you have built in lifesteal, resistances are good in general. For damage items, either something that builds from Sheen (IBG has a nice build path, TF might be a bit too expensive unless you're extremely fed), or Last whisper if everyone's stacking armor. Mostly you want to build full tank since you get damage output from your Q. And staying alive for longer means you get to Q more often. --- lowercase
You don't just Q farm on Nasus and expect to win, it still requires some decision making, contrary to what most people think.
If you bad with Nasus and your team is dying while you're in top farming Q and you don't know where to go or what to do after you have 2,000 Q stacks and near end-game build after you decide to join your team, you'll still lose.
Nasus builds for the most part are mostly situational tank items and then either Iceborn Gauntlet or Trinity force for the Spellblade proc.