A celebrated art historian who has spent a lifetime looking at art writes about looking as a way of being in the world This is not a memoir. It does not take the form of a story. It is instead a kind of self-portrait, or perhaps several self-portraits.   Svetlana Alpers had been keeping files: records of what she saw out the windows of her loft in New York; records of art sold, bought, or seen on her walls; records of foods found in markets and prepared in places where she lived; and records of herself seen in photographs, drawings, and paintings made by others. In solving the question of her father's place and date of birth, she reconstructs the life of her Russian grandfather in a distant and tumultuous Europe of a century ago.   It was Roof Life that made it all come together. The title refers to what one discovers looking out from high windows with distant and distinctive views. In addition, it refers to the way one's attention is heightened and sharpened by confronting things that are unfamiliar, or that are made to appear unfamiliar by circumstances. It describes the immediacy of distance.   Renowned art historian Svetlana Alpers assembles in these pages descriptions of things that mattered in a life that began in Cambridge, Massachusetts, continued in Berkeley, California, and is now lived in New York City. The experience of Europe informs it all.