A 25,000-square-foot penthouse spanning the 15th floor of the 3-year-old Residences at W Hollywood is one of the largest penthouse properties in the world. The $45 million residence—more than a half acre of space—potentially has all the comforts of a sprawling Los Angeles estate. The raw space features many of the curving forms and long horizontal lines that defined the style of art deco, and the residence’s architect, Los Angeles–based Richardson Robertson III, envisions sleek, curvilinear interiors designed …