What were the walls and roofs of buildings made of?

This depends on the building and the date it was built. In the early timber forts the walls were made with wattle and daub which is a wooden frame with clay and mud. The roofs were probably thatched. In the later forts the walls are stone with slated roofs. Some buildings would also just have stone foundations and timber uppers. Thatched roofs would also be common in the later forts.