Carpenter Artisan

You could build a stone keep or castle without the aid of wood scaffolding, but you wouldn’t want to. A woodwright’s frames, blocks and tackle, scaffolding, all help your laborers, making ten men work like fifty. And of course, many of the structures in and around a stronghold are made of or use wood in their walls and frames. A thirty-foot-tall hollow cylinder of stone is a granary. Put some joists, frames, two floors, and some stairs in, and now you’ve got a tower that folk can live in! 
THE CARPENTER’S SHOP: Carpenters lower the cost to build and upkeep siege engines by 10% per level of their shop, and they let you improve your stronghold 10% faster per level of the shop.