As the post said, i want to build weapon cases but I don't have glass...

Go to the general goods stores. Those vendors sell glass, straw, goat horns and such

You need to find the ore or mine it, then smelt it.

just a guess but did you try crafting it using the same materials to craft glass weapons? I think its malachite iirc

* Don't dismiss other members replies, it's flamebait*