Nasus, Curator of Sands is a defensive champion focusing on life steal and Damage rather than hard engage and crowd control.

His build and play style should reflect this, as he tanks through life steal and spell vamp.

For runes concider:

9x ArPen marks
9x Flat Armor Seals for early game defenses
9x Scaling MR Glyphs or 9x Flat MR Glyphs (depending if your opponent is AP top or AD Top)
and 3x LS Quints for more early game sustain (16% lvl 1 no item LS = fun times)

For the Scaling MR Glyphs let us look at the numbers
1.35 MR vs .15 MR/lvl
at level 9 that is 1.35 MR OR 1.35 MR +.15 per level there after.
By level 10 (about when team fights start breaking out) you will have more MR then the other top lane who took Flat MR Glyphs and most of the enemy team at that point. This allows you to tank Magic Damage better than others while still allowing you full defenses vs an AD top lane opponent such as Renekton, Fiora, Darius, and Rengar.

Armor Penetration is nice early game due to the % damage increase it will offer you (8.55 AR pen or about 9-10% bonus damage). So why not Attack Damage Marks if you have 16% lvl 1 LS? The Attack damage marks will give you 8.55 Attack damage at level 1 but this scales off VERY quickly in the mid game. Stick with the Armor pen as by level 4 you will see that you are doing 10-15 extra damage a hit vs the 6 ADM due to the AR/LVL most top lanes get.

Flat Armor seals are very STRAIGHT FORWARD you are taking a lot of physical damage in top lane and need the early game survival. Scaling AR seals would be good if you were against an PURELY AP top (though unlikely due to how squishy mages are). Stick with flat and you are good.

Quintecenses being 2% Life Still is good all game long as the bonus hp it yields Scales with you. An 6% sustain early game is always good as this can allow you to win a trade you otherwise would not.

Formasteries I go 0/17/12

Offensive masteries: This is a Pure tanking build, as such, you will need minimal offensive bonuses.

Defence: Take Magic Resist, bonus ap, bonus armor effect, and flat damage reduction. These will keep you in lane after trades far longer then anything else.

Utility: Bonus mana and hp5 is nice as well as FURTHER increased sustain in lane putting you at a STAGGERING 19% life steal at level 1 with no items. this turns into a base 29% life steal at level

Here is the list of priorities for spells (spaces = reduced priorities)

FLASH - you have access. TAKE IT!

Ignite - Needed early game and sustained game burst true damage

Barrier - Great tanking spell, but you generally will not need this

Smite - Need an extra smite for Barron or dragon? I guess it is better then other options.
Teleport - Great moblity for split pushing, but Predictable at times.

Heal - More sustain, but long CD
Exhaust - Long CD Wither

Clarity - Mana is nice, but you wont go oom if you are smart about things
Clairvoyance - Support only
Ghost - Nice for getting out of sticky messes, but your ult can do that for you
Revive - Why...just Why?

PROS!
HIGH SUSTAIN CHAMPION!
Decent Damage
EXCELENT single Target Slow
Nice AOE
Strong Scaling Auto attacks with Q
Strong Late Game

Cons
Bad Engage
Short Range
Easily caught out of position
No Escape mechanic
CC = Sad Puppy
Slow Start Game

always try to get Siphoning strike to last hit when able, as this will build up MASSIVELY over the game

You should be able to reach 100+ stacks by the end of the midgame

Keep wither up for when you can win long trades with your foe. Soul fire is a great way to lock some one up with the wither on them.