My brother recommended looking at the website http://www.kids-in-mind.com/ to get and idea for a possible way of rating the books. I think it's a great system so I'm going to borrow it. Sex, violence, and profanity will be rated from 1 to 5, 1 being little to none and 5 being excessive. The format for the ratings takes a little getting used to but I think it will work well. For example, Frankenstein would have the following rating: 1.3.1 (The first 1 represents sex-there is none. The 3 is for violence--there is plenty but not graphic. The last 1 is for profanity--this I'm not completely sure about, there may be a very small amount so maybe it should be a 2.) Hmm, as I think about this a little more I'm wondering if I should go to a 10 scale. I just don't want it to get too complicated. Well, I'll start with a 5 scale and see what happens. If 1-5 is insufficient, I'll change it later.
If this is not clear, then please comment and I'll try to clarify.