There was a request for a guide on this. Really this one is targeted for Keep owners, but you can adjust the supplies needed for castles or towers. I plan to do a video walk-through for this as well, but that will be a little bit down the road.
The guide can be found here: https://uohomedecor.com/furniture-2/how-to-create-a-granite-counter-tops-and-cabinets-in-an-uncustomizable-home/
If you have any questions n the guide, please leave feedback on this thread on UOForums.