Nautilus is one of the best engage CC tank in the game. Nautilus has so much CC in his kit and he is super simple to play as well. Nautilus has 4 different forms of CC in his kit.
His first clear is slower than any meta jungler (it's not so slow if you take 2 points in E at level 3). The recent buff to his E helped a bit. You should full clear in under 3.25 with 2 points in E level 3.

Pros

- Lots of CC in the kit
- Very simple kit to learn
- Strong ganks
- Hard to avoid his engage
- Can peel a lot in teamfights
- High burst with low counterplay with all the CC when ahead

Cons

- Falls off late game but not that much with this build
- If you get behind, you won't be that tanky
- Big hitbox, making it easy to get hit by skillshots
- Low dps so still need a somewhat decent team to win
- Easy kit but hard to play in the jungle as you need to hit your Q for ganks (I don't advise him for low elo and beginners)

In the skill order I selected Q second but actually I choose between Q and W based on the game.
If I am having trouble staying alive I will max W and if I just want to push my lead, I will max Q.

Aftershock is very good with this build since it gives some resistance that will scale well with all the Hp from the build and deals damage based on your bonus HP.

You can take shieldbash or demolish based on preference or playstyle.

Conditioning gives "free resistances".

For the last Resolve rune, you can pick the 3 different runes based on your team and the enemy team.

Overgrowth is the standard rune because more tankyness.

Revitalize is good if you have one or more enchanter with heals or shields. I think it might be good if you go Radiant Virtue => Stoneplate => Fimbulwinter for a more defensive build.

Unflinching is good if the enemy has a lot of CC.

For the domination page, I like taking eyeball collection but I think Cheap Shot is good too. I don't know what is the best rune.

I always go for Relentless Hunter because Nautilus is slow so it will help him moving on the map.

Hexflash is insanely strong but need good vision to use well. It opens new gank paths so it's really an unvaluable rune.

The point of this build is to actually have damage and not depend too much on your team to win games.
You will add damage to your full CC kit to target carries and then peel for yours.
It is best in the jungle because you are supposed to gank, the role is especially good to get a lead and snowball.
It's best to invest in some damage early game or even mid game if you are really doing good and try to finish the game as soon as possible by taking objectives.
You always want to take your damage item first and your tank items later because otherwise it's kind of a waste to build damage since you don't scale really well.

The whole point is to get damage early to snowball by ganking, farming more and taking objectives then you go tanky to be able to frontlane for your team and be a CC machine.

Nautilus has a 0.9 (Q) + 0.4*aa (W) + 1 (E 3 waves) + 0.8 (R) = 3.1 AP ratio in his build and 0.4 more for each auto during his W. It's actually really high.
For example, Annie has 2.4 with Q, W & R burst.
Of course she can stack AP easily because she is ranged and not at risk to die in melee range but AP is not a trap on Nautilus.

Here Phreak clearly states that he expects Nautilus to be built AP tank in the long term so my playstyle is already in line with that :
https://www.youtube.com/watch?v=PU4dFDKewMo&t=5205s

Example of builds based on your team comp :

Tank build I think is not so good in soloQ but if you play flex 5v5 it can be decent.
Damage 2/10
Tankyness 9/10
Utility 4/10
Crowd control 7/10


The perma frost build is good if you are not the main tank of the team as you will have more damage while still being tanky and have an additionnal CC.
Damage 7/10
Tankyness 5/10
Utility 1/10
Crowd control 9/10

The ROA build seems to be overall the best build as you have a very good balance of damage and tankyness. Perfect for SoloQ.
Damage 6/10
Tankyness 8/10
Utility 1/10
Crowd control 7/10

For any build, don't remember you are a tank and you can delay your core build to build a specific defensive item.

In the jungle, you get most of your damage from your E.
This skill can actually hit 3 waves each dealing damage (2nd and 3rd dealing 50% damage).
Hiting 3 waves will allow max damage so it is very important to know how to do it and sadly it's not really easy.
You can learn how to do it in this video at 1.55 : https://www.youtube.com/watch?v=nBCPHQ6NWeI.
His E max damage against monsters is 165 / 270 / 375 / 480 / 585 (+ 150% AP).

With his W shield, he is really healthy during his first clear.

At 3 camps, you have the choice to continue farming with 2 points in E or to gank with Q.

With the recent changes to the jungle and the buff to his E, his clear is good enough to take 6 camps before scuttle spawn.
Of course Nautilus is an awesome ganker so you can gank instead of farming.

I prefer to clear top to bot because as a tank, the squishy bot lane is far easier to take down whereas some top laner can really snowball to the point you can't gank them.

You also prefer to play around rift herald instead of the dragon because it is much easier to get solo and when well placed can have a giant impact in the game.

During the early game, you want to gank lanes that are pushed because Nautilus is not really good for dives unless the enemy is low.

You want to run to the enemy laner to auto and root them instead of engaging with your hook as much as possible.
You want to wait for the flash before to press Q.

If possible, I want to run at the target, press E then auto => W for the auto attack reset and wait for the flash.

If you have to engage with Dredge Line then do it, it's just not the best scenario.

At level 6, it is the same. Only engage with your ultimate if you are sure that if will be a kill, otherwise try to run at the target E, auto, W and wait for the flash then Q then your passive might be back again then press R if needed only.
It's really a devastating gank almost impossible to avoid for a lot of champions.

You should also use your hook on the walls if the enemy is close to a wall. It will reduce your Q cd by half and even at level 1 you will have it available to hit a champion during the gank. It's especially good on side lanes as the walls are close to the brushes and your enemies will most likely run through it.

I will continue to improve the guide over time but don't hesitate to leave a comment to give your feedback if you tried it.