Netflix reality series “How To Build a Sex Room” out Friday, July 8. Each episode follows the deceptively prim and proper British interior designer as she meets with various couples who describe their fantasies and ask her to transform a space in their home into a private carnal paradise. “Darling, I’m the Mary Poppins of sex rooms,” Rose, 57, told The Post, referring to her randy bag of tricks.One of her clients, she said, gave her that nickname, which suits her. “I’m very English, upper class, as it were.