Then you have a ☼«rock block»☼. (Or however you name your construction item.)
I guess that would work for rock (or any other <material> block since you can't proccess blocks any further) blocks, but what about raw stone, wood logs or metal bars?
I for one would be quite satisfied with the limitation of only being able to carve constructions made out of finished blocks (you can make blocks out of wood and metal as well as stone, so that's all the common building materials right there. I don't think you can make blocks of charcoal or soap or pearlash and such, but that's fine - it's weird that those are valid building materials to begin with).
You could think of it as a progression of how much work you want to put into your constructions, with more work leading to higher value. For just throwing together a quick wall, or crappy pillars in your mines that you never need to look at again, go ahead and use raw stone or raw logs. For something with a bit more style and permanence, you take the time to carve blocks instead. And for things that are meant to look _great,_ you engrave the blocks. Maybe you could even go further and encrust blocks with gems and other such stuff - line your entryway with walls encrusted with goblin bone, perhaps. Maybe eventually extend the uses of gypsum and the various dyes to make frescoes, or use fabric to line the walls with tapestries and the floors with carpeting.
Consider some of the amazing bas relief and architectural detailing that goes into the stone block cathedrals of Europe, for example. Stone blocks should be a perfectly fine medium for this sort of thing.