I've found that the best way to get a hold on the castle building/classification is to quantify existing castles.
Study the floor plan, look at some dates, and write down for the points one each ring of defense.
Use the list posted on site.

Then, please send it here, and we can discuss it.
I'll post a list of samples on the site.

You can see (and maybe disagree with) my own samples in NB.
OR, I will list some of them here, when I have some time.

--Greg