I've managed to find a good indicator of what sections the library is split into, what it looks like, and roughly what it contains.
However I can't seem to locate a basic floor plan, such as which floors contain what. I know this seems pedantic but quite alot of this story is set within the Library itself, and I'd like to get it as correct as possible. So if anyone can provide information on that I'd be incredibly great full. Of course any other information on the library itself you think might be useful or interesting would be more than welcome.
Search terms used: Belfast Central Library, Belfast Central library architecture, as well as consulting wikipedia.
Articles I found particularly helpful (even if they didn't answer my question) in case of future reference: Government site containing opening hours and other basic info, General article on the libraries architecture, Wiki article.