Most of us have some idea what Napa Valley should taste like, but what should it look like? Vineyards dotted with stately chateaux, mansard rooflines, Ionic columns, perhaps the occasional turret? Maybe go postrnodern and high tech? For architect Howard Backen, the shape that defines Napa is the barn—simple, open, tied to the land and the agricultural heritage of the area. With such disarmingly plain insights, and the homes and wineries that stem from them, his imprint on the Iook and feel of Napa in the past few years has been tremendous. These high-profile, low-glitz designs emanate from an unassuming white farmhouse tucked into the complex that surrounds the Merryvale winery on Highway 29, just south of St. Helena. It could be mistaken for some relic of another era waiting to