SCHOOL ADDITION 'GROWS': This 70x41-foot multi-purpose room is part of a three-classroom, "L"-shaped addition being built by the local Schoolmaker, Inc., onto Pittsfield Public School's Mary D. Mitchell School. The addition, excluding equipment, is expected to cost about $160,000 when completed early next year. An eight-foot upper portion of the multi-purpose room is to be glassed-in. Facilities will also include an auxiliary classroom, library, offices and special service room, teachers' lounge and boy's and girl's locker rooms. Both Ann Arbor and Pittsfield district voters will go to the polls Tuesday to vote on annexing the latter district to the Ann Arbor system.