So I've decided to make Nasus my main "jack-of-all-trades," because I have him and he's bad ass, and I'm working on turning runepage one into a Nasus page before I complete my Shaco page because a Nasus page is far cheaper:

Armour Pen in Red, 17 Armor pen early game is a good advantage.
CDR/18 in Blue
Health/18 in Yellow, so I can shirk off some HP items late game
Flat Health Quints for the HP advantage.

I've been maxing SF then SS with one point in whither and Fury w/e it's up, but I'm thinking of experimenting with max SS first.

For builds I go:
21/9/0 - DPS Spec
or
9/0/21 - Tanky Spec

with Flash and Cleanse or Ghost and Flash

For items I like:
Ruby Crystal or Sapphire Crystal + 2 HP pots
Lane until I can get Catalyst + Boots + Vamp Scepter
Next Time I recall and get Emblem of Valor + Sheen
Build Phage & Glacial Shroud
Turn Catalyst into Banshee's around level 16, rush it if their team is CC heavy.
Build Triforce
Build Starks
Get Ninja Tabi or Merc Threads
Build Guardian Angel
Upgrade Glacial Shroud to Frozen heart
Keeping a fort pot up at all times.

Most games I get:

Banshee's, boots, Starks, Triforce, part of glacial or part of guardian angel.

Final Build looking like:

Banshee's
Merc Threads or Ninja Tabi
Starks
Triforce
Frozen Heart
Guardian Angel

This way I do enough damage to be a threat but am tanky enough to not get instabigged. http://leaguecraft.com/builder/Nasus...4c8a4b4a54d90d

How do you guys build Nasus?

Tri-force, warmog's, boots of swiftness / treads / tabi. Situational after that.

Or if I'm going straight DPS I'll rush sheen then build boots of swiftness, a bloodthirster, then maybe last whisper and frozen mallet if the game isn't over yet.

usually run

sapphire + 2 hp pots
upgrade to sheen asap and get merc treads asap
then it depends on the game

banshee veil/guardian angel/frozenheart/starks depending on the aura you need and all that jazz

or another build ive been experimenting with is late game nasus
sapphire crystal + hp pot/mana pot(PLAY CONSERVATIVE AND JUST FARM LIKE HELL)
tele back as soon as you have 1850 and grab 2 avarice blades and lvl 1 boots
continue farming with spirit fire
upgrade to sheen
and then same build as above pretty much, you get your stuff faster and can crit some nasty SS early since I have crit damage runes.

Instead of avarice blades get HoGs if you want to farm up.

doesnt synergize at all, i dont want armor lol

my rune page is almost entirely crit damage, the avarice blades help with that.

SS
Fire
SS
Wither
SS
Ult
SS
Fire
SS
Wither
Fire
Whatever else in the order.

Slows are ridiculously good for killing, and having just level 1 so early on does it. Also, you can swap the first fire with wither if you want to gank quickly, but frankly I'm just hitting with SS so often. Average game gets me at least +150 on SS, then I rush a Sheen and make an educated decision from there. This means I'm not pidgeonholed into Damage or Tanking, and can work what's needed. You need staying power in a fight to get full effect of your Ultimate. You also do not want to get disabled. Otherwise, more damage to hit harder as a Burst Damage hero rather than a sustained damage. (SS - Whack, move around, Repeat)