The roof leaks. The library lacks modern technology, and the science labs are inadequate. And every day the original, 54-year-old boiler works properly, the custodian says a prayer of thanks. So is it time for a new Natick (Mass.) High School? The Massachusetts School Building Authority has chosen Natick as one of 49 districts to potentially warrant a new school, and voters will be asked at the April 8 Town Meeting to authorize spending $250,000 on a feasibility study about whether such a plan makes sense.