Frankly, Shyvana is a real bruiser to me, edging more towards tanky than damagey due to her mechanics. I'd roll with either 21/9 or 9/21, utility is wasted. Imo, build towards Wriggles/mercs and then into some health since I find her damage and survivability severly lacking pre-12. Rushing a Wit's after threads f.e. is imo a bad choice. I'd say phage / giant belt -> damage is a better option. Try getting atmogs (or mallet/atma) straight after though, then you become a force to be reckoned with. Due to the way her abilities work in teamfights you'll be wrecking aoe havoc as is, you don't need to build full damage for that.