If you have not used it yet I suggest you download Google Sketchup free version and then look for some plugins to add. But the basic version would probably work for what you are doing without any plugins. There are you tube instructional vids on how to use Sketchup. As a matter of fact there was several on drawing a tiny trailer cabin. Honestly Google Sketchup is easy to use with only a little practice. You can then get screenshots of views by pressing “prt scr” key which copies the screen to they paste bin. Open up PC Paint and paste into it. Then draw a box around the image you want for your book and crop it. Next save it as a file type that you may use in your book.
On my blog on my log cabin article, my green building article and DIY metal buildings article I have some examples on display at the top in galleries. These are some design concepts that I’m working on. I still have a lot more to do to those. It takes a bit of practice and watching the vids but you can get your dimensions exact if you want. Honestly Sketchup is far simpler and easier to use than anything like Autocad.