what is considered “similar suitably sturdy materials” for Galder’s Tower

Galder’s Tower states

You conjure a two-story tower made of stone, wood, or similar suitably sturdy materials.

What would qualify as "similar suitably sturdy materials"? The relevant definition of sturdy is "strong enough to withstand rough work or treatment." Assuming "similarly" sturdy, could the material be extremely hot stone? Would Mythril or diamond qualify under this?