I am not looking for modern tank armor layer-wise. I am just going to take the superalloy (not the ceramics), melt them and then put them into a 4-inch-thick full plate. That would be the equivalent in both weight and toughness to 10 inches of steel or so. I am picking the really dense metals because of mobility - if the armor is too thick, it is going to be really unwieldy.
In comparison, the heavier tank armors today are equivalent in toughness, at least for the first couple of hits, to 40 inches of steel. That is due to the advanced ceramics and reactive explosive layers they use to dissipate hits from main tank guns. However, that kind of armor degrades rapidly against repeated hits, even from relatively lighter weapons like RPGs
The suggestion of using some supernatural with skill in armor-making is a good idea. Instead of trying to do the armor as a mundane item, we could add a few supernatural goodies into an IoP like the following that the giant in question could spend earned refresh to get, using the whole forging thing as a flavor justification;
Armor of Talos [-1]
Made by magically forging heavy metals taken out of wrecked armored vehicles, this suit of armor is one of the heaviest in the battlefield.
* It is what it is: a 30-ton, giant-sized full plate. It has armor rating 4, can only be worn by giants or similarly-sized humanoids and requires an effective might score of +16 to lift and wear effectively.
* One-time discount
* Superdense material: the armor is made of really dense metals and is better able to absorb physical punishment. +1 armor vs physical attacks, a further +1 vs ranged piercing attacks.
* Energy Resistance: the material of the armor is extremely heat and corrosion resistant and acts as a faraday cage. The wearer gets +2 to defense rolls vs such energy attacks.
* Runes Protection: lots of warding runes have been carved onto the armor, providing minimal resistance to magic. The wearer gets +2 to defense rolls vs direct magical attacks.