“The outside is the new inside,” said Peter Arnell, chairman and chief executive of the Arnell Group in New York, an advertising agency that has branched into design. “It’s all about sensory experience. The retail theater closes the deal,” said Mr. Arnell, who once studied architecture with Mr. Graves. For one advertising client, Reebok International, the Arnell Group designed a flagship store in Philadelphia meant to personify the company’s new Rbk footwear and apparel line by converting, as Mr. Arnell put it, “the beats and rhythms of sports into a three-story retail space.” And Jacob Arabo, aka Jacob the Jeweler, the purveyor of bling-bling to the hip-hop aristocracy, is getting an Arnell Group design for his first store, at 48 East 57th Street in Manhattan, which is intended to invoke the interior of a gem mine.