early game:

Nasus is not very stong in the early game. For Nasus the early game is a farm game.So you ignore the enemy top laner,the only thing that is important is farming. you onely attack the enemy champion when the jungler ganks or you and your teammates are in trouble. All you have to do is lasthit with your Siphoning Strike. Make sure that the river is warded so you dont have to fear the enemy jungler. Shurelya's Battlesong is a good farming item. Because of the regenerations and 10%cooldown reduction. The Iceborn Gauntlet is for your Siphoning Strike and more armor. Most people buy the this item because the bonus damage of Sheen.

mid game:

now is is a little bit harder to farm because sometimes your team starts teamfights (mostly mid).so you stay with your team and farm the jungle camps. But sometimes you can farm top too.Because you have to stay a life in teamfights.I recommand a Warmog's Armor for health and health regen. I olso recommand the Black Cleaver is gives armorpenetration 10% cooldownreduction and and health. this i team is one of my favourite, because it is a very good buiser item.

late game:

Finally you can choose between many items with 10% cooldownreduction like Banner of Command Locket of the Iron Solari Spirit Visage Zeke's Herald Frozen Heart I prefer Locket of the Iron Solari vs AD teams and Spirit Visage vs APteams.Now it's teamfight time. it is very important that you are in every teamfight. You have to be the first in the fight, because you are very tanky and you make tons of damage.

early game:

my jungle route:
Wolves
Blue buff
Wraiths
Red buff

Make sureyou lats hit 80% of the monsters whith your Siphoning Strike . when you gank try to Witherthe enemy first. because your Wither has a low cooldown. Spirit of the Elder Lizard is a good jungle item. Because of the damage and faster jungle. I olso recommand the Locket of the Iron Solari is gives armor health regen and cooldownreduction. The Iceborn Gauntlet is for your Siphoning Strike and more armor. Most people buy the this item because the bonus damage of Sheen.

mid game:

now is is a little bit harder to farm because sometimes your team starts teamfights (mostly mid).so you stay with your team and farm the jungle camps. But sometimes you can farm other lanes. The Warmog's Armor is a great item for this. Because you have to stay a life in teamfights.

late game:

Finally you can choose between many items with 10% cooldownreduction like Banner of Command Shurelya's Battlesong Spirit Visage Zeke's Herald Frozen Heart I prefer Shurelya's Battlesong for more resistance and Spirit Visage vs APteams. Now it's teamfight time. it is very important that you are in every teamfight. You have to be the first in the fight, because you are very tanky and you make tons of damage.

10:00 min +100 farm damage
20:00 min +200 farm damage
30:00 min +300 farm damage
40:00 min +400 farm damage
50:00 min +500 farm damage
60:00 min +600 farm damage
...

: Garen has an extreme melee damage and is's hard for Nasus to farm. whe he Decisive Strike s you, and then DEMACIA.
: Evelynn is very effective against Nasus. Beacouse of her Hate Spike and her Dark Frenzy Nasus goes down fast.
: Teemo is ranges and it is difficus to get in range to attack Teemo. When you now in range you get Blinding Dart and killed.
: Rumble is one of the most hardest solo top laner ever. Special for nasus beacouse need need to get in range to farm Minions. but when he trys it he get Flamespitter
: Riven is olso to a to strong memee champion and when she plays good she know how to stop a Nasus farm.

1. Dont let Nasus farm. When he is solo top your team must gank him very hard
2. Quicksilver Sash or Shurelya's Battlesong are good items to escape his Wither
3. good stuns
4. You must have a Very good tank
5. When you are a ADC and the enemy Nasus is strong i recommand to buy a Frozen Mallet

Renekton
Shaco
Kayle
Volibear
Cho'gath

My runes are armor and magicresist. This runes help me to stay longer at laning phase. And live longer in teamfights.

just like the runes :)

My Items are very tanky. with tons of resistance and the best 40.00% Cooldown reduction. whith 40% you have your siphoning strike all 2.4 sec :O

I recommand to max Q first. I think that makes everyone :)
But the question is why i max W second and not e ?
I thins it's better to max an effective slow second. Becouse the spiritfire is not to strong and the wither is mor effective.

Teleport: for better farm when you go back to base.
...
Ghost:for better chasing

In ranked i think it is better to play jungle Nasus. because the enemies in ranked now how to couner nasus top and dont let you farm.

Pros:

very tanky
extreme damage
high cc (slow)
loow cooldowns
can carry a team
can fight (sometimes) 1vs5
good mana pool

Cons:

week in early game against ranged carrys
relatively slow
item depended