The goal of this build is to gather as much Health, Ability Power, Attack Damage(based on health stat), Armor and Magic Resistance as possible (in that order). This set of items supports a tanky Nautilus with enough damage to support the team. It's important as Nautilus that your team is following you into fights; you must ult the squishiest enemy at the back for the knock up and group disruption. My favorite targets include Brand or Ashe since they tend to run back toward their team when they're being targeted, leading to a whole team being knocked up! Once the enemy team is soaring through the air admiring the view, your team has the opportunity to deal all their damage and slay a few of the baddies before they're able to move again.

I shouldn't need to explain any of this to you. Here are the items and my reasoning...

Grab a Doran's Shield because it has that sustain you want in the early lane phase. Follow up with a Regrowth Pendant for some more sustain, unless you want to go straight into a Ruby Crystal or even a Heart of Gold.

Early game is complete.

Boots. Mercury's Treads for the tank on your gift list...

Your next move depends a lot on what your team is up to. If you have a support building Aegis of the Legion, get some armor from something like Glacial Shroud or even Thornmail with an Attack Damage heavy team.

Your most important items are Rylai's Crystal Scepter and Atma's Impaler.

After those key items, there are quite a few options.
Warmog's Armor is a great health boost and health regen item. (plus you were already building it with that Regrowth Pendant) ;)
Rod of Ages is useful but don't ever be tempted into rushing it first. It's a weak starter. Take it late game for the extra Health, Mana, and Ability Power.
Abyssal Mask is good if you have enough AP coming from your other teammates to make it worth your while.

At this point you should decide if you're lacking in a specific statistic. If you didn't take a Thornmail earlier, you might want a Guardian Angel at this point. A late game option for you to consider is selling your Aegis of the Legion for a Guardian Angel. That should be your last item if anything because you're opting out of buffing your team, to the greener pastures of reviving after death. Choose carefully. Also if you need to recruit more Magic Resistance because you didn't buy that Abyssal Mask, pick up a Banshee's Veil

Items I don't ever want to see on Nautilus:
Frozen Mallet might boost your health, and slow your enemies with each physical strike but...
Rylai's Crystal Scepter already does that and more! Spells are everything for

This is what your late game build should look like:

Mercury's Treads
Aegis of the Legion
Rylai's Crystal Scepter
Atma's Impaler
Warmog's Armor
Rod of Ages


Replace the Aegis of the Legion with Guardian Angel or Thornmail depending on the situation.

Replace Rod of Ages with Abyssal Mask or Banshee's Veil

You will be good to go. Happy diving!