Do NOT use Marble Armor

[NTJedi]

Gandalf Parker said:
Isnt that why that robe of invulnerability makes such a point in its description about being perfect for casters?

Since casters quickly get fatiqued the protection provided quickly becomes worthless. There's many other armors which are better for casters if you want them to survive.

Robe of Invulnerability is good for the fire king who already has ethereal if you plan on making him a SC. Due to the gem cost... there's a few better options.