Is it necessary to build separate rooms within bathrooms to shield oneself from jinn?

There is no need to enter a separate room within the restrooms to hide from the jinn. The Sunnah for one entering the lavatory is to say: "Bismillah (In the name of Allah)," based on the Prophet's (peace and blessings of Allah be upon him) saying: "The screen between the eyes of the jinn and the private parts of the children of Adam, when one of them enters the lavatory, is to say: 'Bismillah.'" A person protects himself from Satan by remembering Allah the Almighty.