Colin, as a conservation architect and having built a few buildings over the years, I'd have to say that GNR has the most modular of all styles.
Station masters houses, signal cabins, platform shelters, all follow a defined pattern. They are also the most difficult to reproduce, such is the level of detail.
MGWR might appear austere in its design, but it ranks second when it comes to buildings and patterns.
Anything in the GSWR world is a mess. You can see stations on both sides of limerick, Croome and Pallasgrean come to mind, and they are wildly differing styles.
If you like a building, build it, rename it, and cherry pick other buildings from other stations as needed. The right effect can be achieved. Richie.
Edit - I have that shaffrey book, the rendering of Thurles is lovely.