I tried the extra 2% movespeed while out of combat and extra 3% movespeed from 21 into utlity with movesped quints and I was laneganking like I was a freaking powerballing rammus, kinda squishy though but jungle is no prob due to passive.
"Warwick are you jungling" "No I'm standing by the wolves because I miss my family"
Standard start for Junglers with machete 5. If you spec into the jewish masteries, starting with a ward can be beneficial since Nasus doesn't really need more then 3 potions to sustain him early on. Max E first is a no-brainer: Your clear speed is awful if you don't. From there, you can max Q second if you want to be selfish and farm Q more, or go W for more teamplay. To clear most camps, just E them, Q a smaller monster immediately, then auto the large one until your Q can finish it off. Spirit fire + bladed armor should clean up the smaller monsters.
Ganks are pretty simple: Just use your crap. Nasus' ult is better for sustained engagements rather then chasing, so keep that in mind. Ghost is pretty much a must on Jungle Nasus, Nasus' ganks are pretty strong since Wither is redic and can still result in a kill even if they flash and he contributes ok damage as well as (previously before the turret buffs) being fairly tanky for tower dives. He's fine at clearing the jungle too as it helps him farm his Q and he has alright clears, so don't feel like you're forced to gank or that your ganks are lacking and you should just farm: You can really do either and be fine.
Wither in teamfights is best used on right click champs obviously. This usually will mean the enemy ADC, but can also be used on people like Jax if your team needs peel. Keep in mind that your Q won't be as farmed in the jungle as it will top lane, so your Q should be dealing decent damage but not completely demolishing everything. At any rate, you should be running after one of their carries and trying to kill them. You should be fairly tanky and be capable of taking quite a bit of punishment, so don't be afraid to go deep.
As for the build, I don't really know. Aegis and Bulwark if need be are pretty much core and should be gotten every game, but past that it changes depending on how much damage you want to be dealing. Gauntlet is basically the best offensive option, so if you want to carry get that. An early Philo into Shurelia's is a solid option if your team needs more initiation. Spirit Visage is a great MR option, and Frozen Heart is a good armor one. Even locket is a good choice. Honestly, anything that gives CDR and tankiness is good on him. Don't go too gung-ho on expensive offensive options (Like triforce) though since your gold is limited in the jungle. Honestly, I don't know whether to go spirit stone or madred's. I've seen pros go both, but madred's will screw up your Q farm.
Overall, Nasus is a great tanky champ with the new changes to him, and the jungle, although limiting his Q farm, fixes his greatest weakness which was his horrible early-game. Nasus is actually a fairly good Jungle 1v1er post-6 with all of his stuff up, although a weak one without his ult, and using a full rotation of spells drains a ton of mana. He's a great choice for any team that's looking for a little more beef from their jungle but can still deal respectable damage.