Nasus, in my opinion, is one of the most underrated champions out there. By underrated I mean, you never see him. I see one in every 15-20 games. When I do see him, he's never any good. This guide is to show you the Tanky-DPS/Roamer side of Nasus and face-stomp every one that comes in you way.
The Skill section is huge. (Close to the 5k minimum by it's self.) Read through it anyway. Some of the things are important.

I'm going over the skill's "skills"/skill order/"correct" way to use skills here.

Abilities

Soul Eater: Your passive which gives 15/20/25 life steal. It's not a great passive until you start to Siphoning Kill everything.


Siphoning Strike:Siphoning Strike is your best skill by far. If you are bad at last hitting, you will fail hard with this. It resets your auto attack timer so you can effectively last hit a you just hit once you know you attack animation's speed. Doing this is crucial to learning to stomping with Nasus. It snowballs fast and effectively into late game. The bonus damage it gives your attacks, also works on turrets.


Wither: Wither is your one and only form of CC. It's also your only spell that will break a Banshee's Veil bubble. If you hit people with this, it applies an initial slow to both move speed and attack speed along with an extra slow over a few seconds. Coupled with the speed you have off this build, people will not be able to escape. It also doesn't pull turret aggro so, it can buy you a few extra seconds to push a turret.


Spirit Fire:A nice bush checker/stealth deterrent. Lowering armor of things standing on it is a nice bonus. Combo it with Siphoning Strike and your passive life steal, you have a nice heal over time. It does a deceptively good amount of damage. Sometimes netting you kills just for laying it down.


Fury of the Sands: You ultimate and the skill that really makes you fit into the Tank/DPS role. Giving you bonus HP and dealing a percentage of all nearby enemies' HP per second and adding to your AD for a while. This is not a skill to be taken lightly. Using it correctly could mean the difference between death and surviving a 5v1 gank. (This happened to me. I died because I turned around and got cocky.)

Skill order

In ideal situations, you want your skill order to be Fury of the Sands> Siphoning Strike> Wither> Spirit Fire This will make sure that your ganks are as strong as possible. If you end up needing to farm in the jungle, change the order to this: Fury of the Sands> Siphoning Strike> Spirit Fire> Wither to make sure you are healing for as much as possible off the jungle creatures and moving through them fast.

"Correct" Skill Usage

Siphoning Strike:

• Do last hit with it active.
• Do use it to quickly push turrets.
• Do use it in combination with Fury of the Sands or Spirit Fire if possible.
• Do use it whenever possible when fighting Baron/Dragon/Buffs
• Do use it to nuke down opponents.

• Don't use it just to slightly damage enemies other than champions or super minions.
• Don't trigger it unless you are coming to a minion line or camp with enemies you know you can one-shot.

Wither

• Do use it on a fleeing enemy.
• Do use it on an enemy to pop a Banshee's Veil bubble if your caster is readying up all their most powerful spells.

There's not much you shouldn't do with Wither. Just don't randomly use it if you know you or a teammate can't get a kill off it.

Spirit Fire

• Do use it to de-buff people during team fights.
• Do use it to help you farming of Siphoning Strike
• Do use it a slight stealth deterrent. (Saved a Sona with it a couple of times)
• Do use it to check bushes.
• Do use it in combination with Wither and Siphoning Strike for more damage.

• Don't use it as a form of harass.
• Don't use it if you won't have enough mana for another skill.
• Don't forget about it when stealth-able melee champions are involved.

Fury of the Sands

• Do use it in the middle of many enemies.
• Do use it to escape surprises if needed. (Yes, 5v1 ganks are an acceptable surprise)

• Don't use it while fighting the "big" buffs unless you are "surprised". (Dragon/Baron)
• Don't use it whenever it's off cool down.

If I use the term "rush" incorrectly, excuse me.

Buy a Dagger and head to lane. you want to be rushing a Zeal for the move speed. Even though most other champions will be faster than you, your Wither will keep most people away long enough to make the fights 1v1 for a bit.

After buying the Zeal, buy a Sheen simply so you can farm your Siphoning Strike just a bit easier. Rushing Phantom Dancer and then, Boots of Swiftness will start off your roaming game.

Rush a Trinity Force grabbing Zeal before Phage for the extra move speed. After this, you want some tank items. Your close to 1.5 AS and the Trinity Force proc off Siphoning Strike will give you all the extra damage you need.

If you are dying a lot, buy Guardian Angel first. If more team fights are going on, buy Aegis of the Legion first. Get the other one soon after.

The final slot can be filled with whatever you want. If you feel a little slow, buy another Phantom Dancer. Feeling focused by casters, Banshee's Veil is your item. Anything other than that, experiment with what's best for you.

Runes are a fairly important part of playing Nasus. Most of the runes are yours to chose but, what I list works for me.

Primary Marks

Greater mark of Desolation
Makes your Siphoning Strike hit like a truck early game when you need the life steal the most. These are non-negotiable.

Primary Seals

Armor for the early game tanking. These are fairly negotiable. You can take whatever will gave you more staying power in lane. Don't get mana regen runes though. You have Clarity for this. Don't get the HP regen runes either. You passive makes up for this.

Primary Glyphs

Flat CDR runes because all your skills, other than your ult, are on fairly short cool downs and only Siphoning Strike gets a lower cool down as it levels. Somewhat debatable. If you want, you can take MR glyphs to make you just a bit more of a tank.

Primary Quintessences

Greater Quint of Avarice
I use money Quintessences. These are completely up for debate. I take them because once I start roaming, it becomes slightly hard to earn money if you can't easily kill things. If you don't want these, take whatever you want. Maybe flat HP, ArmPen, or something else.

In general, don't take these rune types if you can help it: MP5, HP5, AD, AP, or any scaling runes.

Take Clairvoyance because, you will be wandering around the map and this gives you great map awareness. If it is active and you don't need it currently, check bushes with it or check one of the major map objectives. The masteries you get will have it on a close to 30 second CD.
Clarity is mainly for early game and for whenever you can't get blue buff. It also works nice for when you need to sustain a push with a partner.
There are very few alternatives I would suggest.
Things you shouldn't take: Smite, Ghost, Rally, Revive, Heal
Anything else is fine but I don't recommended it.

Taking a 0/9/21 mastery set will give us just what we need to have a ton of lane presence while not sacrificing too much.

The dodge mastery is to give you a slight bit more tankitude. The move speed bonus is just a bonus. Splitting up the 4 points needed in the first tier of the defense tree gives us a bit more defense towards either form of attack. if the other team has more of one kind of attack, move those points around accordingly.

Extra EXP and GP is needed so you can stay caught up in levels and cash. Once you start roaming, your team will start having a nice level advantage if your team isn't terrible. In this tree, relocating points from anywhere other than Meditation is probably a bad idea.

I would post pictures of this in action but, my router is being an *** and I can't connect to the League of Legends server to take SC of it. You can look at my match history if you want. Name is in the profile. Try it! You'll like it.