I would pick Nasus against forgotten top laners which falls off late-like Gankplank, against few early-mid snowballers like Yorick or Chogath, if everything else like: jayce, rengar, riven, vlad, shen, malph would be banned (actually i think i'd maybe pick Nasus over Shen since he's overrated imo->ppl don't know how to play Shen and they are picking him no matter what if he's open->even for support).

Build:
Let your opponent push-your lane is supposed to be gank paradise for your jungler, and 100% dive hell for enemy jungle. Don't die pre 6, stack 2 gp 10 items. If you're winning get Trinity Force 1st. If you're loosing get Frozen Heart 1st (if you're against ap, get mercury treads asap). Tri Force and Frozen Heart are your core items. Later on focus on aura items for your team, since your true strength is stacked Q, R, and W on enemy ADC. Don't forget about Guardian Angel->just to be sure that they will pay if they focus you and somehow kill you.

Priorities:
1. Stack Q.
2. Farm.
3. Cover your ADC.
4. Kill all the things.

Others:
If I'm playing against Nasus I'm doing everything to make him use his Q on me, not on minion. Don't do that. Someone is attacking you? Go away, leave 3 creeps, let minions push, Q to farm, no to harras.

Spells:
1. Exhaust
2. Ghost
3. Teleport (you shouldnt leave your team 4v5 because you have to stack your Q more and Shen just dissapeared from your lane->if they loose mid and bot, u won't carry this, you are not katarina or akali). Consider taking it against strong sustain/harras, like Yorick. (over ghost, u need exhaust more, and u can always get shurleyas)
4. Ignite. If you rly think that you will be able to kill things on your own or if Soraka in enemy team.

Runes:
9x as red
9x armor yellow
9x mres blue
3x ms quints

Consider taking gp10 quints over ms. You can always drop as for bonus armor/dmg.

More sections & explainations will be added. This is only a short blueprint.