Somehow, I think Ito Junji-sensei also write almost exactly the same stories.

Well no, not really. I mean yes, but actually those stories are quite famous. There are many versions and all. Like fairy tales, everyone knows about the story and make the story with several changes. I don't know about the story of the man in the attic but the story about the chair is pretty famous . It's the story of a rich woman buying chair and the chairmaker became the chair . You can't say it's copied since Ito Junji-sensei also copied (with several changes) the story to make it his own.