What special considerations, features or requirements are important in this type of architectural commission?

Palladio’s Villa Rotonda, Le Corbusier’s Villa Savoye and Frank Lloyd Wright’s Fallingwater were all designed as country retreats—what today we would call “vacation homes.” What special considerations, features or requirements are important in this type of architectural commission? How did each architect respond to his clients’ needs (be specific)? What is similar and/or different about the solutions the three architects arrived at?