It may seem at first glance that there are absolutely no grounds for thinking the narrator is mad. Rather the complete opposite appears true: that the narrator is the one point of sanity and rationalism in the utterly sinister, foreboding, decaying house of Usher and its similarly deteriorating owners, Roderick and his sister Madeleine. Roderick's statement that the narrator is mad is usually just taken as another sign of his own disturbed mental state. However, a more subtle line is taken by some critics of the story, who speculate the narrator may be less straightforward than he appears. Some critics have suggested that he might be unreliable as a narrator, that he may be hallucinating when he sees the final ghastly appearance of Madeleine, or indeed that he may even have conspired with Roderick to get rid of Madeleine. Therefore, he might not be quite as sane as he claims. And, even if he is quite sane and reliable as a narrator, it is true that he can't altogether escape being affected by the utterly dark and gloomy atmosphere of the House of Usher - although he does manage to flee from its final destruction.
actually, i believe that the author was not mad at all. Since Roderick knew that madeline was not dead the entire time, he thought that the narrator was "mad" or crazy for not knowing something he thought was so obvious.