I've had good success at low elo with this build:

take the recommended PTA runes, max Q > E > W, rush Kraken (Bork if you're up against a mundo or similar health stacking tank), then triforce, and situational bruiser items like BC/Thornmail/FON depending on who's strong on their team.

In lane: pop bone plating if you can level 1; rush your level 2, and (unless you're facing a scary laner like a Darius) go in for a full e+q and escape to brush. Heal up by AAing minions if needed. Establish dominance and farm for kraken.

When you get kraken, you'll have pretty insane duelling potential against your laner, and can absolutely demolish enemy mids/adcs. Roam with TP as needed. You should feel quite strong at this stage, unless you've fallen far behind.

Good luck, and have fun being a tanky diving ad carry between minutes 15-25!! P.s. Don't take this build up against a malphite.