Interesting art concepts.
If they were to use stone as a building material you would need to find something that would survive battles and stress fractures.
So they could use huge iron nickel meterorites.
Some huge silicate life form's carcass.
They could grow a large crystal and build a ship off that
These are natural crystal systems that grow in nature.
Attachment:
Crystal Structure and Crystal System 2.jpg [ 76.41 KiB | Viewed 6276 times ]
If you like a shape and incorporate it into a design it would be cool.
Another material is Jade specifically Nephrite due to its interwoven, fibrous crystals this makes it extremely tough and durable. One reason it has been used throughout history as a tool as it can take blows that would just shatter other types of stone.
This would have to be painted on the model but then you could use any shape you like.
I know realworld vrs scifi but why not.
Cheers