Below are two images from my Monkey Island project.
Before starting on the model in the real world, I'm building it in my computer using Google Sketchup. It's a great (and free) 3D modeling program from Google.
Thirty years ago, I would have begun the model building process by drawing up a blueprint on paper, but computer generated 3D modeling is a much stronger tool.
Although very rough, you can see I'm starting to develop the basic shape. The idea here is that I'll be able to use this computer model to create a card paper rough model of the castle that I can then add clay details to, finishing the model.