You get free boots at 10 min. but you cannot buy boots before then. These boots give additional MS. For each takedown you acquire the boots 30s sooner.
Nautilus is one of the premier users of Aftershock thanks to his numerous forms of CC. His passive, [Q], and [R] with all grant you the bonus Armor and MR for surviving trades/all-ins.
Shield Bash synergizes incredibly well with Nautilus' [W] for additional offensive and defensive power.
Conditioning provides incredible mid-game tankiness that allows you to front-line and apply massive team-wide CC for your team.
Overgrowth's health scaling pairs well with Conditioning and makes you a formidable front-line tank. The extra mid of health also synergizes well with your [W] shield
Biscuit Delivery is a fantastic sustain option for tank champions in lane any. The Biscuit heals for a % of your missing health, so if you proc it in a fight when you're relatively low you'll gain massive regen.
Magical Footwear's easy gold efficiency makes it a great support item, allowing you to hit your Locket power-spike that much sooner.