Outdoor rooms are like stage sets in a theater you build around your own life. A garden enclosure heightens feelings and associations dulled by indoor routine. It plays with your sense of time and space. Small acts, ordinary events, stand out. In the fine old garden of Barbara Chevalier, stagecraft has a prominent place, not in the sense of staginess — no dying camellias or fussy topiary here — but as design. A few simple concepts wed nostalgia and practicality, structure and fluidity.