Gnar tips?

Hey everyone. Can anyone give me tips for Gnar? I've looked at probuilds and guides and there's so many different way to setup runes and masteries. Some people go for CDR, others go for AS. Which is better in which situations? After testing a lot of different things, I have found this to be the most effective: 3 AS Quints 4 AS marks 5 AD marks Armor seals Scaling MR glyphs 15/15 masteries (Changing the last 6 in def depending on what I lane against)

And for build I go for hexdrinker first vs an AP lane, BC vs anything else unless I need to kite (Like for example vs Garen or Darius) Then get BC, then pure tank. Is there anything I should be doing different? Any advice would be great.

Edit: Is sunfire better than Randuin's? And is Warmogg's worth getting with the changes? I've heard so many different opinions I don't know what to believe