Just remember when you read about castle that you decide what kind of style you want to go for.
There are tons of diffrent castles.
- Celtic castles
- Scottish castles
- Medieval castles
- Viking "castles" (Rohan is based on this)
- Chinese temple design
- Middle eastern castles
There are alot of diffrent styles, so it depends on the landscape you are painting what kind of castle you should design. If you put it in a desert environment you need to look into why castles work in a desert. And why a castle can work up in cold scotland aswell.
This i guess is about makeing your painting beliveable to the viewer, cause if you would place a concrete/mud castle in scotland it would be strange. Or build something out of stones in norway, or make it out of wood in a desert....
Be carefull about it hehehe