Greetings summoner! What masterpiece shall we play today?

More siriusly, Greetings fellow summoners! this is my first build here on mobafire, but i'm a long time reader of all your contribution, so thanks in advance for reading and thanks for the good work!

I 'm testing ap Nasus for some weeks now, and i find him very versatile and powerful. I will update this build if i have time, but he is actually viable on Vi's patch.
Personally, i prefere going top with AP Nasus, contrarly to a lot of them going mid, because i think a good AP mid (AoE is better) can add a lot to the destructive power of your team.

Preferably some AoE disable, or AoE damages (a jungler Amumu), a galio mid, a Nunu & Willump bot support...

Having someone beside you who can tank damages is a good thing too, because after some team-fights, enemies will begin to notice you and to focus you.

A Sivir bot can also help a lot thanks to her ult.

Soul Eater PASSIVE: 14/17/20% lifesteal, procing on your Q, allows good sustain and trade early game, can be hell of a heal if you buy lich bane (the magic damages of lich bane proc it too, not sure why)

Siphoning Strike Q: your identity as an AD nasus, but still farm it well (and it helps last hit!)
in trades, AA before using it because it refresh AA timer

Wither W: the spell that will piss of a top darius or vi, the thing that make you unkillable, THA MOFO 95% slow! ganked? W on top, Exhaust on ganker, byebye =)

Spirit Fire E: your bread and butter, you are pushed under tower ? -> E
you want to push ? -> E
you want to harass ? -> E
you want to scout bush ? -> E
you want to deny creeps ? -> E
you want to slow ? (Rilay needed) -> E
Beware of the mana cost, but normally with masteries, runes, 2 dorans and sheen, you should be able to spamm it for a while.

Fury of the Sands R: that R... enemy low life under tower? W -> E -> Q -> R -> bye bye
enemy towerdiving you ? W -> E -> .. wait... ho it's the same :)

In line, it's a very effective tool to finish of a scared enemy under tower and escape the jungler alive, to survive a gank under your own tower, or simply survive ( Exhaust + Fury of the Sands + Wither, no way to die)

In team-fights, you become a giant dog god who melt his enemies and cannot be focused because of his tankiness. remember to slow the two carry, to place your E Spirit Fire, hit your Q Siphoning Strike on that fleeing (with 95% slow) ADC and ALWAYS be in the middle of the mess.

Pros:
-tanky for his dps, great suvivability due to his Fury of the Sands ult and Wither slow
-great pusher ( Spirit Fire lvl 3, 1 spell = 1 wave)
-awesome AoE damages (late game can melt half the enemies health in 2-3 seconds)
-not focused in early team-fights (free kills), focused on midgame/late teamfight, but hey, you are fed and way too tanky now
-creeps OVER9000 (rich $_$)
-CAN COUNTER Darius AND Vi top O.O
-trade very well early after Sheen ( Wither W + AA + Siphoning Strike Q + Spirit Fire E, they will go back instantly)
-scale very well into late game due to % damages ( Fury of the Sands)

Cons:
-mana dependent early Spirit Fire
-push maybe a bit too much if you want to harass Spirit Fire (not really a problem tho)
-if shutted down early, comeback is hard (but possible due to awesome creeping capabilities Spirit Fire)

What i really like with Nasus is that i don't need gank, thus i can let bot and mid get ganked and improve our chances of win a lot. An AP Nasus doesnt't need kill, because he will farm so much, and deny enemy top so much, in team-fight that alone is already a big difference. Add to this the multiple ganks from your jungler on other lanes, and you got a large margin winning mid game (thus late game)

Against non dangerous melee champ, farm Siphoning Strike Q as much as possible, keep the creeps in the middle of the two tower (avoid unwanted ganks), poke with Spirit Fire E.

Against ranged champ (or teleport champ ( Master Yi, Akali, kata)) Casually farm and poke with Spirit Fire E, ward your bushes, push them under tower to deny creeps (you can poke them under tower due to range of Spirit Fire E)

If you see enemy jungler in another lane and enemy is < 30% life, Wither W him, Fury of the Sands R Spirit Fire E Siphoning Strike Q take kill, back regen mana life and spend your hard won 300 gold.

I really like to play aggressively because people expect that i will passively farm my Siphoning Strike Q and be a farm fest, whereas i deny their creeps hardly, and often take kills within 10 min. Surprise surprise...

REMEMBER TO USE YOUR Wither SLOWS! if ganked, or need to escape. don't hesitate to use Flash and Fury of the Sands ult either. A hard escape can be done by Flash > Wither / Exhaust the gankers > Fury of the Sands ult to survive in case of unwanted skillshot or ult > Spirit Fire E to make them suffer for what they did

later on, just go to any lane, Spirit Fire E, take 10 creeps, repeat.

If you are against a troublesome top (darius, yi, vi), push with E , deny creeps, slow if they try to come to you and flee like a little girl (a midlife top coming to you mean the jungler is not far)

Early - mid:

If you, the top, enter team-fight, you must have at least boot lvl 2 + Sheen + 2 Doran's Ring, it's the minimum to survive out there. Try to Wither W that annoying little skilshotter ( Ezreal, Nidalee) Fury of the Sands ult (don't be afraid to use it, its duration is very (VERY) long) Spirit Fire E Siphoning Strike Q. If your team follow, he must be dead, if not, Exhaust the main DD, try to be in the middle (you are faster than most due to materies + runes)

Now, either they focus you, go back to your team slowly so your Fury of the Sands Ult continue to dish out damages, replace Spirit Fire E, use Wither W on the most annoying one. If bad comes to worst, Flash out (you already did your job, they should all be < 50 % life, 1 should be dead, when your team is full (except for you)). If entire team is under tower and low life, don't hesitate to go full in (if > 50% life) because 1) there is good chance you can kill them all with Spirit Fire E + Fury of the Sands ult and 2) if not, you tank and your team do it (4 assists :3)

Till there, it was easy.

Mid - late:
Now, you should have a LOT of creeps, some kills and a lot of assists too (depending on your aggressiveness, and your presence on team-fights).
You should have boot 2, rylai's scepter, Liandry's Torment, 2 Doran's Ring, and a situational item (if not Lich Bane, sell a Doran's Ring for it (if you suffer a bit, Rod of Ages or Sunfire Aegis are good choices, as they give you suvivability AND dps))

You can now almost instant kill any squishy crossing your god's path ( Wither W AA Siphoning Strike Q Spirit Fire E) (especially with Lich Bane)

Don't engage full life team-fights, you have an AoE Slowing poke (+ with Liandry's Torment, it burn 10% max hp of enemy team)

When someone is near 50% HP, or they are all +- 70% engage (W + exhaust carries, Spirit Fire E R Siphoning Strike Q (on of the carries)). right after engage, they should now be +- 50% ( Spirit Fire E + Fury of the Sands ult + Liandry's Torment hurt) stay in the middle, Siphoning Strike Q the ones with lowest life (remember to spam, 3 sec CDR) Flash out if bad come to worst, let your team finish em off, (or if you are not focused (or have a Zonya) GO FOR THE PANTA, IT IS FAIRLY POSSIBLE (done two this week))

Sorry for the lake of images, i will try to update this as much as possible.
Thanks a lot for reading! Don't hesitate to say whatever is in your mind, or give me advice =)
(Note that I'm not a native English speaker, sorry for the grammar mistake =s )

tl;dr -> ap Nasus rocks