Nasus is well known for being a hard to kill champ then when well farmed puts out a ton of damage. This build is not trying to change this but to capatalize on this by featuring a ton of damage while still keeping that tankiness that Nasus is known for.

Also this is my first build guide so please be gracious.

Pros
-Passive gives great early lane sustain
-Q is rediculous if farmed well early game
-W lets you stick to a single target or get away from one
-E gives good armor reduce to help captilize on your Q
-Very tanky even in team fights letting your team focus down the squishies while you
whittle down the tank

Cons
-Failure to farm your Q will lead to a poor late game
-Mana will run out very fast
-Cant deal damage to groups
-Easily out ranged with CC

Passive-Soul Eater

Gives base life steal causing Nasus to have good sustain.

Q-Siphoning Strike

This skill... this skill is the reason I tried Nasus. This skill simply add bonus
damage on hit. However every you finish an enemy with it, it will gain 3 more damage.
So you kill 50 minions with it you get 150 more damage. Late game this move has
terribly high damage if you farmed it well.

Capatalize on this move ASAP for more damage and CDR as you want to last hit with this
skill as often as possible.

W-Wither

This spell is a single target heavy slow. It does no damage but it still is one of the
greatest slows out there. It starts at a 35% and increases up to 95% at level 5 over 5
seconds.

Take this spell after siphoning strike to stick to your targets or get away from a
scary opponent.

E-Spirit Fire

This is an AOE DOT spell that does a fairly pathetic amount of damage. However enemies
in the radius of its effect get reduced armor.

The armor shred is useful so take a point in this early but max it last.

R-Fury of the Sands

This is Nasus's Ultimate and that it is. Upon activation Nasus recieves bonus health
and starts dealing AOE damage based on the Max HP of the targets up to a cap(you wont
reach the cap with this build) and that AOE damage is siphoned into bonus attack damage.

As with any Ulti grab this whenever possible, this spell you want exclusively for team
fights but you can use the bonus health to escape a bad situation.

CORE ITEMS

Guardian Angel
This item gives good armor some MR and its passive will save your *** so many times. This
item is very important to the build.
Black Cleaver
This item gives decent AD and AS but the big thing about it is the passive with level 5
spirit fire you can reduce someones armor by 85! This item will let you tear through
tanks that you will likely be dueling.
Phantom Dancer
This items AS bonus is amazing the 30% Crit is nice and dat Movement speed is oh so
helpful. this item will let you be a lot less sluggish. Since your gonna eat all ton of
CC this item will really help you out.

Varible Items

Boots of Swiftness
I highly suggest this as Nasus is a bit slow and this will let you stick to your prey.
Alternates
Mercury Treads-If you are getting a ton of CC get these
Ninja Tabi-In case you need that little extra armor.

Force of Nature
This item gives mad hp regen good MS and very nice MR.
Alternates
Phantom Dancer-If you aren't seeing much AP from the enemy this item can be a better
choice.
Aegis of the Legion- Need more Armor and not MR well Get some anyways but this will
a little bit of all you need.

BloodThrister
I hear you say "Nasus already has life steal." However more is better and this item gives
massive AD as well.
Alternates
Madred's Bloodrazor-Maybe you some more armor and want to do more damage to tanks.
Grab this.
Infinty Edge- If you got the second Phantom Dancer this will make you a scary opponent.
Frozen Mallet-This item gives you HP, AD, and it slows your target. A good choice when
enemies are kiting you a lot.