You can make as many computer models as you like but there is no way to properly choose materials without getting a good load of samples together.  These are gorgeous hand made Kent tiles for a new build in West Sussex that I am completing the construction detailing for.  The new house will mostly be hidden away behind a wall and the roof is going to be the main visible feature with a mixture of historic and contemporary detailing.  The sketches show the development of the detailed design that has been carefully worked out to make sure everything is lined through, lapped, overlapped and tucked in correctly.  It is important not just for the appearance of the building but also its durability.  The timber and tile setting out includes drip details to shed water onto the face of the boards and junction details to protect the more vulnerable end grain where possible. This all ends up as setting out details so that the builder will know how to put it all together.  This sort of architecture does not needs to shout and most people will not notice the detailing.  When it is done it should just look like it was always meant to be like that.