Hi this is my first write up of how i play nasus. I firmly believe he needs a mixture of tank and damage items to reach full potential. Also using the cheaper component items to have a linear increase in power is one of my goals here instead of large jumps that rely on large sums of gold. This build works best with a classic tank in the team but is able to be the sole tank. I will admit that with this build I have trouble combating Kogmaw and other percentage health champions but with solid dps around you and focusing those champs you can come out ahead.

I find that the above runes give me enough mana regen for only infrequent btb as long as you are conservative with wither and reasonable with spirit fire. The other runes are just for an early lane advantage and really can be swapped with your favourite runes.

again this area is really flexible. I choose ghost and clairvoyance as they are spells im familiar with and sometimes i mix them up a bit. other good spells include exaust, rally, cleanse, and ignite. I prefer being able to use the clairvoyance to look for incoming ganks when I push a lane and supporting my team with map awareness. Other masteries are just my preference. i need the extra mana regen. I dont tend to take neutral buffs so I dont take that mastery. I like the surprise effect that the extra speed from a dodge gives. Match it to the way you play.

additional:
Just realised that I have no dodge chance anyway so there is no point for evasion woops.

There are 2 schools of thought that I have seen in the nasus builds. 1)max out siphon and leave spirit fire for last or 2) max out spirit fire first with some siphons and some wither. I believe that the skilled player can time the last hit of the siphon well enough and can get better benefit from the farm effect of the spirit fire. That being said I usually take 2 levels in siphon for the larger window it grants. You need to use siphon liberally every time it is up find something to last hit with it. wither is a fantastic ability but I usually find that its first level is enough for the early and mid game and the longer versions arent needed till late game. Spirit fire can be thought of as a harvester in the lane. At lvl 5 it can pretty much kill caster creep outright and it is great for tower hugging. Never forget that it also drops the enemies armor while they stand in it so choose the placing carefully in team fights. "Oh so you think you can stand in my purple **** do you!"

My philosophy is every time you are back at base you go out a bit stronger. Never save up for a big purchase. always blow your money on the components of the next thing you want.

Justification

Warmog
reduces the need for high resistance
the higher resistance you get the less return they have for gold output

randuins
tons of armor enough to get you to over 150
the extra aoe slow is gold but remember to use it
heart of gold is cheap and gets you tons of gold

force of nature
highest mag res item in the game
regen your lovely warmog health in the blink of an eye
enough to hold off the worst of madreds
makes you run fast and chase punks down
combined with merc treads it gives you over 150 mag res

sheen and trinity force
if you play nasus without sheen you hamstring yourself
it expenentially increased your damage output
goes so nice with siphon making it easier to grow
scares the **** out of squishy opposition with great burst damage
great for dropping turrets
trinity force is really expensive and should be delayed until you are tanky
if you get off to an amazing start sure get it earlier and keep the ball rolling
trinity force is like another sheen on top of your sheen

atmers
this one is just fun


There are a few situational items that I use as well.

Quicksilver sash
If they have malz or WW, or heaven forbid both, this come into play. only item that breaks supress. This will drive them nuts and have them screaming OP. It actually works better on your squishies.

banshee
I would grow the ruby crystal into the warmog first if they dont have much dps and then get a banshee later in the build instead of randuins. I still like force of nature cos it gives such a large increase in mag resist.

Anyway this is how I play:
-Once i get the randuins I can run in amongst the team on my own and drop one and severely hurt the rest. With team mates behind they are in trouble.
-As with any build you need to be prepared to adjust to the game as it unfolds.
-You need to find a way to get fatter faster then the other guys and keep doing it.
-dropping towers is more important than the score board!

glhf