Seeing as you are a Castle fan, I would suggest you use the wall elements available in that theme like:this
or maybe this
and of course this one
And any others you may have.
Have them studs up, or laying on their sides, even inside out. Any windows in the parts can easily be used for windows
or filled up with some minor plate constructions, which could be the base for some greebles.
Good luck whatever you do.