A lot of people play AD Garen in URF, but personally I find tank Garen way more fun. 
In URF, Garen's W at max rank gives 41% damage reduction for 4 seconds, and the cooldown is only about 2.5 seconds — it's a straight up busted ability. So I've been enjoying tank Garen with Heartsteel, Jak'Sho, Unending Despair, Force of Nature, Randuin's, and Spirit Visage.
Thanks to the 0.75 seconds of Tenacity on W, he handles CC reasonably well too. Plus with the healing from Heartsteel, Jak'Sho, Unending Despair, and Grasp, you can keep your HP up — his sustain is absurd.
And because of Jak'Sho and Heartsteel, mages and ADCs get chunked to lethal after two or three Qs and an ult, so unlike other tanks, he can't just be ignored — makes him that much more annoying. If you get Garen in URF, give it a shot.
Runes and summoners are the same as Yoon's URF Garen video.
Grasp, Shield Bash, Conditioning, Revitalize Transcendence or Nimbus Cloak (your preference), Celerity
Pretty sure that's what he ran.