If you do want to take it to the next level, I do believe that creating the terrain in a 3d modeling software would be your best bet. Using a program like Blender can really enhance detailed items, such as the stone in this particular case.
I’m not too sure what exactly you’re asking – but there are quite a few different tutorials and guides floating around the internet on how to create detailed, realistic terrain in Blender for use in Roblox.
A video such as this one, looks like it could be helpful. I would spend some time doing some research!