Any site trying to do something like this is going to be very dependent on the work of others. Indeed all I have really done here is read a few (hundred) books and looked at a few (thousand) web pages and organised them in a fashion which I hope is helpful.
Each individual castle or other building is given its own full bibliography and web links listing but there are also a considerable number of more general books and links used in the composition of the site and some books and sites that deserve a fuller description. For easy of use I've split my sources into a bibliography of written sources and a listing of web sites.
I've generally excluded mentioning at all books or sites which don't meet a minimum standard. If I mention a book or web site I think it's worth looking at, my negative comments are general those few things that make a source less than perfect, rather than what makes it not worthy viewing.