I belive that if u just do ad shyvana u die very quick in teamfights. And if u are tanky shyvana u are almost unkillable, because then u use this build u have something like 300 ad 4600 health u can make evry ad carry champion 1vs1 because your abilites.

A tank are the one who gonna get up the team in team fights so even if you are tank the enemy want to focus you because your damage output and evryone in your team want just the tank die huh? I have get pentakill 1vs5 with this build and are pretty proud about that.

Shyvana can do top lane very very very good because her tankiness and health regen she gets.
Bot lane: if u have a carry in your team that are very weak and die easy shyvana help them out and the best it's if u are bot lane with a ranged carry.
And the last ''lane'' u can play with her is jungling.
Jungler: shyvana goes pretty good with jungling she are a good surviver in jungling and do so much damage with her q and w.
I do not recommend shyvana mid because u almost have no ranged spells so u do almost no dmg there.

I suppose to have thormail because even if they are some ap in the enemy team they almost deal no dmg to u before they die ;). but if they are more then 50% (if they are 3 people or more in 5vs5 or 2 or more in 3vs3) ap in the enemy team, u switch thormail to force of nature.