I'm so excited about this project now. Yet more great work being done!
I agree with Jachyr's idea about the materials (it was his concept after all).
Would it be possible to incorporate Senten's idea of brightly coloured glass windows (reds, greens, blues, yellows) on the model?
Here are some textures I found which would might be suitable for the stone walls:
http://www.tradeinteriorsdirect.com/cheltenham/images/Sandstone.jpg
http://www.chinagranite.us/stones/Sandstone/Yunan%20Yellow%20Sandstone_S.jpg
http://www.castiastone.com/colors/images/Sandstone.jpg