Ornn's item upgrades seem like a bit of a missed opportunity (suggestions for improvement).

Mere stat increases just makes them seem really bland, not to mention lacking in value before late game (1000 gold for 30 AD isn't worth it when you could spend 900 for a vamp scepter or save up a little for QSS or Zeal).

I suggest removing (or lowering) the bonus stats, and instead granting them improved effects.

Since Ornn is a demigod of the forge, who lives and breathes fire, burn damage seems the right route, thematically at least.

Enemies who try to break the shield are burned, taking 25% of the damage they dealt to it over 3 seconds (burn damage cannot exceed the value of an individual shield from this item) Aura range increased to 600, deals double damage to champions. Can be toggled off. When magic damage is amplified on a champion, half of the bonus is dealt to everything within the aura over 3 seconds. Critical strikes cause the target to take (15% total AD) true damage over 3 seconds (multiple instances stack). Abilities deal 8% of their magic damage again over 3 seconds. Enemies caught in the active radius take the damage again over 3 seconds. Enemies with max stacks take 5% bonus physical damage as a DOT. Procs deal an additional (50% base AD) as true damage over 2 seconds.

As far as power goes, I think Ornn is actually fine. He (and his items) just need to be more satisfying than "here's some stats".