OK, a lot of guides say this, and i will to.
This is my first guide! when i started playing, i was deciding what character to unlock with my 1350 ip when i saw nasus. id always loved Egyptian things, so it was destined to be!
so i unlocked him and played my first match with him. i loved him ever since.
what i love about nasus is that depending how you play, he can be a powerhouse in the early game, a real terror mid-game, and the reason your opponents surrender in the end.

now the reason i pick those runes are as follows.

mark of desolation. this gives ar-pen, which is really important to nasus as his key source of damage is physical. so these are a no-brainer.

seal of replenishment. this really helps nasus throughout the game, especially early, as it gives him enough mana regen to ALWAYS have all of the mana he is ever going to need. when i started playing i had mana starvation issues, especially early game...that doesn't happen anymore.

glyph of focus. these provide cooldown reduction, just under 5% of it. this means that combined with your masteries, you start the game with a base 14.89% cdr! (lets just say its 15%). then, once you get nashors tooth your cdr is pretty much maxed. sweet!

quintessence of swiftness. these provide movement speed. nasus has high movespeed as it is. BUT, with that in mind, what if other people seem unnaturally talented at running away from you? these have helped me more then any other quintessences, i find, because it means people are NOT going to escape from you. assured earlier kills, run fast enough to save a friend, it's all good!

Here comes the skilltrees!
the key parts to these masteries are the cdr. cdr is god on nasus, as it makes his q more spammable, which shows in his damage in two ways. first, you can get more last hits with q, making it more powerful, faster. second, it provides more casts in longer fights, and against a tankier character who REALLY wants you dead, that can give you the edge you need.
the rest is really just filler that i thought the most useful, if you want to then feel free to play around with them, this game is all about how you play your character.

Now we get to the fun stuff!
what you start with is always up to how you play, but i think its always good to atart with a dorans shield. nasus doesnt have much armour at the begining of the game, so the armour will help as well as the hp and regen.
lets start with out shoes, shall we?
boots of swiftness i find to be the best in the majority of situations. however, if you are up against a cc heavy team, feel free to get mercuries, or if against ad carries then ninja tabi may make an EXCELLENT choice!

trinity force is practivally a must on nasus. simply for the sheen proc. 150% really helps you last hit things...like other players! the attacks speed is nice, the move speed marvelous, the damage and health arent too bad either, while the mana helps keep you out there, knocking heads for longer!

now this is the part that gathered me a lot of hate, and then later, confusion.
nashors tooth. the first thing this does is max your cdr. making your q the biggest threat it can be. second, some mana regen and enough spellpower for another 1% of damage on your ultimate! taking into account the sheen of course. then comes the attack speed.
whats your primary source of damage when not using q? auto attacks. what does your ultimate do? raise your attack damage. a lot. so you need as to take full advantage of it! thats why nashors tooth is a beautiful choice for nasus.

now that we have our damage sorted, lets stay alive long enough to use it, shall we?
warmogs armour. health, health, regen and more health! some people say your ulti gives enough hp to tank, but it just isnt so! you get burnt down just to damn fast! so this is to give you that much needed health, wich is where the next two items come in. making it count.

the last two items arent listed, because they arent absolute items. it all depends on the composition of the enemy team. a balanced team may call for a force of nature and a randuins omen, while an AD heavy team would just hate you for a thornmail and sunfire cape.
in short, the first three items are to make you the owner of anything you touch.
the last three are to make sure you dont get owned yourself.

now, some people may be confused as to why i dont put any points into soulfire untill i have to.
thats because it pales in comparison with your q and wither! wither slows people so ridiculously much you should always make it close enough for them to guess your cologne, and siphoning strike...i dont even have to explain that one. if i do, then go PLAY nasus, then come read this guide. your ulti should be taken as soon as possible, for obvious reasons, and spirit fire gets taken once you have everything else. its useful, just not as useful as your other spells.

the first summoner spell is ghost. it helps you chase, it helps you escape, it helps you engage and it helps you save people. a wonderous spell for nasus.
exhaust also helps, for the fact that wither has a short cooldown.
when you get attacked by 2 people at once, you will know what to do.
hit the AD carry with wither, slap this on the next most relevant person, then let them taste your staff!

my idea for this guide was to get the way i play nasus out there, because i dont see many good nasus players ever. and it makes me sad.
the endgame for this guide ends up with with an quite tanky, crazy-damaging egyptian god-card nasus...assuming you farmed your q right throughout the game. im not going to get into the specifics of HOW you should play, because when to chase and when to back off are things you have to learn for yourself.
ill try to keep this build updated, i may forget about it.
let me know what you think, and then go forth.
go forth, and farm your q!
p.s sorry for lack of images XD