Scorp had seen Rose in the library many a time, and when in the common room, she had also been doing the same thing.
Reading.
So, every special day in her life, he would buy her a book. It came to the point where Scorp gave her a book on 'The Day James Potter Tidied The Burrow' or 'The Day I lost my Revision Sheet', and Rose didn't have any more space.
So on her birthday, Scorp added a room (with the permission of Ron and Hermione) onto her house. It was a beautiful library, and it was the best present she ever received.