NOTE: THIS BUILD IS UNDER CONSTRUCTION, PLEASE NOTE REVISION IN YOUR COMMENTS.

Nautilus is a great tanky hybrid to have on your team because of his insane crowd control and great scaling with his abilities. Jungle Nautilus is a very strong gank because of his slows and his passive bonus makes it incredibly hard to get out of his gank once he hits the first Dredge Line. This build makes him able to absorb massive damage while still dealing out loads in his abilities and his basic attacks.

The runes used in this build is mainly based around utility and overall durability for early game resistance.

MARKS
I used cooldown reduction marks because Nautilus's abilities have incredibly high cooldowns and this helps for stronger ganks and ability spam.

SEALS
I used armor seals to help give you more early game ad durability for stronger ganks against ad carries.

GLYPHS
I used magic resist seals to give you better resistance against ap carries so their abilities do less against you.

QUINTS
I used health quints so that you get more health against everyone so you are more scary early game.

0-21-9 Masteries work great with Nautilus because he gets extra tankiness over his normal tankiness while giving him better mob resistance in the jungle so that he doesn't take as much of a beating from wolves and wraiths early game.

These items give you a great damage output while keeping up in good magic resist and armor and giving enemies trying to counter Nautilus the need to buy not only armor, but magic resist items also, reducing their item slots and how much damage they can do.

FAQ

Why not CDR items?
I didn't choose cooldown reduction items such as Nashor's Tooth because I believe that his cooldowns do not affect him as much when you get to late game team fights.

Levelling up your Shield first goes hand in hand early game ganks, also making enemies have to focus you to bring down your shield so you don't do as much damage from it, letting your carries devour the enemy team in the process.

Your E is second to be levelled up for it's slow and damage, making ganks strong and countering melee enemies that focus you.

Lastly, your Q which will give enemies a hard time when they take a ton of damage as well as being pulled towards you.

Flash
Nautilus has a below average base movement speed which makes it so that getting away needs to be easier if you get caught out. If used correctly flash can give you an extra kill or deny the enemy a kill on you. Using flash in combo with Dredge line can give you great getaway skills.

Smite
This helps you clear jungle camps and gives you 10gp every time you smite. A must-have for a jungler.

Nautilus is an all-round great jungler with strong ganks early to late game and a good amount of health, armor and magic reist to make him a hard target to kill by any champion.

The route I take for jungling is

Wolves -> Blue -> Wraiths -> Wolves -> Red -> Golems

This should give you a good level to take on any jungle camp and gank strongly

PROS

• Very tanky
• Deals a lot of damage
• Has hard CC
• Once he's Dredge lined you you're pretty much dead
• Can be built to play any role (with pros and cons for each role)
• Hard to counter with a good team because of his hybrid hard CC build.
• Strong ganks and counter ganks with dredge line and his hard CC
• If played correctly early game he doesn't phase out for late game team fights, pushes and defences
• Hard to kill without getting caught out, even then if done well you can dredge line out of bad situations

CONS

• He's generally quite slow compared to other champions, but you can make up for it with a nicely placed Dredge line to terrain or an escaping champion.
• Relatively easy to dodge Dredge line, but once caught you're pretty much dead.
• Dredge line can't be cast over terrain which makes escapes very hard, but probable
  

If you're against fast/mobile players with low CC swap out Merc treads for boots of swiftness, this will make your low movement speed less of an issue if you get caught out or get focused in a team fight.

When a team fight looks like it's about to happen, if you're confident that you have a strong team with a good carry and everyone is strong enough to fight you should initiate with dredge line. This should case the enemy team to focus you and will also pull out a major part of their team so they can be pulled apart one at a time (Just make sure you don't dredge line the tank, otherwise it would be pointless as he should be initiating for them). It doesn't matter if you become the focus of the battle, this is because you should be tanky enough for you to survive until their team gets torn apart by your team or at least get rid of their main damage dealers you are killing you. In times like these you should use your shield as a source of damage absorbtion rather than for damage like you would do when you initate a team fight.