Go tank build. Contrary to what people might say to you, Nasus is easily the most effective as a tank.

Doran's Shield
Chalice
Ninja Tabi or Merc Treads
Heart of Gold x3
Sell one, buy Aegis
Sell another, buy Sunfire Cape
Sell another, buy Banshee's Veil or another Sunfire.

Use the chalice to constantly spam spirit fire and rack up the most creep kills in the game. Use siph strike for last hits and try to play conservative if you are getting harassed hard.

Max spirit fire-wither-siph strike, and obviously pick up your ult every chance you get.

I agree with the premise, but not the build.

Start with Ruby Crystal. (or regrowth, but I like ruby because it builds into aegis)
RUSH aegis. Before boots1.
Build merc Treads
Build Sheen/Phage->Trinity Force

If the game is not over, look and see what you need. Sunfure is great for armor+HP, banshee's for MR+HP, etc.

Skill build:

Spirit Fire First
It's an amazing skill for the level 1 team fight, and even if you don't get in the team fight it's amazing for laning.

Siphoning Strike at level 2
This is your threat, it;s what makes people want to focus you. You want to get it beefy.

Wither at level 3
because it's a snare.

So your skill build should be this:

E
Q
W
E
E
R
E
Q
Q
Q
R
Q
E
W
W
R
W
W

Laning: Use E on the minion group, last hit things, get as many last hits with Q as you can. At level 11 you become a beast with your ult, the level 6 version isn't -as- amazing.

When you engage a team fight you want to make sure they start fighting back before you blow your ult or they can just back off. Make sure to spam E during team fights too, it lowers armor which makes your team hit harder! (the damage is nice too, I guess)

Runes: HP and Mana regen.

Spells: I like Rally and exhaust, but clarity is also pretty good. If you go clarity shift your runes to nothing but HP.

no matter how you build him, play very defensively early game by not pushing too far into the minion battle except to land last hits with SS (which you should do as much as possible). don't waste SF until it's around level 3, it won't help much until then. when SF is at a decent level use it to farm minions as it'll pretty much ensure last hits on almost all minions. i don't think that anyone can farm as well as nasus can now that corki's valk got nerfed.

Exhaust is for the blind effect, not really the snare. You can spirit fire spam with clarity, which is what I run most of the time. I would rather rush an aegis then waste time with Hearts of gold, and I don't see why you would -not- get trinity on Nasus. It gives Health and a supersheen for SS.

I wanna nip this sh*t in the bud, and it's been pissing me off for quite some time.

Siphoning Strike's last clause reads "Siphoning Strike's damage increases by 2 when it kills an enemy" or whatever, I'm not sure verbatim. But the message is crystal clear: Last hit with Siphoning Strike on cooldown, and Siphoning Strike gets +2 damage. Correct me if I'm wrong, but is this how it works? If not, why does it read this way? I recognized Sion's Enrage ability has the same mechanic, except it adds to your max health points. I've also recognized that Sion's last hits with Enrage toggled on DO INDEED increase your maximum health points, every single minion or champion kill. I've monitored this very meticulously. So why can I activate Nasus' Siphong Strike, last hit 4-7 minions while it's on cooldown, and not get a single +2 bonus from any creep kills? Is this a glitch, or am I just horribly misinformed? And if I am, I wish Nasus' q ability's wording would be permanently corrected.