I LOVE Nautilus, he is a titan of CC-tanky-damage goodness, really cant not overstate how phenomenal he is when played correctly. Also he has the best dance in the game.

Runes/Masteries, pretty standard for me since I play too many champions to have ones specialized for each champion I play. Focus on maxing CDR(I go a bit over on this build but I prefer nashor's to morellio's as Nautilus has very low attack speed and draws a decent amount of damage from the proc damage he hits for while titan's wrath is active.

Summoner spells are the ones I always pick I have a hard time justifying anything else, and then, only when I jungle on summoners rift do I put in smite normally.

As in any dominon game things move fast and you need to be pretty flexible on your item build in order to win. Above is generally what I aim for, a mix of tanky/ap items, focusing on flat magic pen because I find it is cheaper to reduce my enemies magic resist than build high AP items. Generally for this purpose I pick sorcerer's boots over merc treads, if I find the enemy has too much CC I buy a moonflare blade(usually as my third item), cheap, ap, tenacity, zen.

Obviously if the enemy team has some serious AD for you to deal with you will want to grab a thornmail instead of hourglass.

Next pick either the nashor's or the haunting guise, both are solid items and not too expensive. I find moving up in items quickly in dominion is more worthwhile then saving up for big ones like deathcaps and such.