Nasus's strength comes from his ability to farm Siphoning Strike. Try to zone him or deny his chance of last-hitting minions. If u play nasus try to farm with Q,and dont let them haras u.
If u have hard spammer on top,just try to farm and wait for lvl 6,after that u can control ur lane,and stack Q for late game.

Life steal rune are god for nasus,for early,mid and late game. If u build hydra and spirite visage. U will have 46% life steal,and thats a sick heal for a tank.

More Armor,more Magic Resist and Health points are god for nasus ulti and turret dives.
Goal for this build is to stack Q,tank turrets,kill ap or ad carry.
One tf and push is all u need to win a game with this build. Trust me ;)

Best thing for nasus is help from a jungler,if nasus kills his opponent before lvl 6 he will get full control over top lane and overfarm his Q.

You`r team needs to understand that Nasus needs to be "afk farm" ,till 15/20 min in game. Or he will be easy to kill in mid or late game. Bear with him when his on your team,and he will secure your win. Stay as longer as u can on your lane,so that he can farm and own in mid and late game. ;)

Nasus is the most easyest camp to carry ur game.

He can kill 2 champions with one blow!
In team fight always use Wither on there marksman,that will cripple a bit,and u will have time to kill thers ap carry if his feed.

If u stack only Q and W,that will help u and your jungler to gank top. Easy gank and kill on top.