Here's a little guide to building a classic. By classic, I mean a solid castle base that many people know about. From this type of castle, people change the look of the castle to suit their own taste. All the same, all castles will end up looking like this one. So no one will be able to say you have a bad castle with this type of castle.
Personally, I use a heavily modified version, but for the purpose of the guide, I'll stick to a simple case. With your future experiences, you will change your castles.
For those who wonder, I used the following program to make the pictures