This is my first go at a build so please try it before you trash it, because it is unorthodox and I have soo many people rip me in game before they see how much damage I can dish out and take after I build my armors.

I take these because the armor allows you to shrug off most minion damage especially with your lifesteal. I also find that the masteries allow massive damage especially when you can land siphoning strike while they are in spirit fire. They also allow you to farm with spirit fire as it eats health away and lowers armor.

I use spirit fire as a way to keep enemies away from farm and to kill the caster creeps while I siphoning strike the melee creeps. Siphoning strike scales in power from last hits so you don't need to level it early, the amount of damage you get doesn't outweigh the pushing power of spirit fire in a 1v2 lane. Although if you are against a champion that is making life difficult and you aren't getting your siphoning strikes often enough then you can put an extra point in early but make sure you have Wither at level 3 otherwise you are an easy gank.

Honestly I hardly ever get past the Force of Nature. At that point you are doing so much damage and AoE with Spirit Fire and your ult which feeds your attack power most champions can't compete with your power. Although there are times when you are being focused and are dying you can always build armor earlier and get the Bloodthirster and Infinity Edge after the 2 armors. And I know warmogs is just health so a Guardian Angel could be subbed in.

I find that Flash is good for escaping with wither, and Ignite or Exhaust depending on if your team has any Exhausts. But really these are personal preference.

Well most people don't get cloth armor and 2 health pots and 2 mana pots, but with this spirit fire heavy casting build. When 1v2 or until you can bully them out with a Wither, Spirit Fire, Siphoning Strike combo this is especially damaging INSIDE the spirit fire ring because it lowers armor values.

For boots you get Ninja Tabi for AD and Mercuries Treads for AP.

I then rush trinity force getting Sheen then Phage then Zeal.

At this point you can hold your own against all but the most fed Champions so if your team is winning and you want to continue to dominate you go Bloodthirster then Force of Nature. this gives you more sustain than they can handle and your AD is huge. Although if you are losing you might want to go Force of nature first and buy the regrowth pendants first if it is an AD champ wrecking your team or the negatron cloak if it is an AP champ.

After those you need to see if you need more health from Warmogs or more Damage from Infinity Edge.

I've seen a lot of people say that Nasus isn't good at initiating team fights but I think that he can assist in the initiation. For example somebody not their tank is out of position up front, you can use Wither to slow that person so your tank can go in or a burst damage ally can cripple that champion. Which leads to a 5v4 team fight or that person stays in the back and it is like a 5v4.

But Nasus can initiate a team fight by using a tactic that most wouldn't. I have used this to great success when the other team is lacking a true tank and has another Nasus or a Mordekaiser. I simply wait for that awkward milling about waiting for the other team to make a move thing and simply hit 1 with a wither then flash in the middle Ult it up to get the AD bonus and AP buff then use Spirit Fire and spam all abilities like normal. Most teams are surprised at you doing this so it may take a little bit for your team to come into the fight but it makes no difference if it is late game and you have your damage items and health regen. Now dont do this if your team isn't there or they have a real tank that has some serious CC.

Overall this build is different but effective and can turn Nasus from a tanky bruiser with 15+ assists into a carry with 15+ kills and the other team not wanting to go near you without it being 3v1 in their favor.