Workers with nail guns were busy finishing the reroofing of Stilson Elementary School and portions of the new air-conditioning system were running Friday as the new principal, Tanita McDowell, talked about her job and the school where she greeted children and parents at a Thursday night open house. Changes at the prekindergarten through fifth-grade school in the Stilson community 15 miles east of Statesboro are examples of those over the summer in the Bulloch County school system. More than 10,000 students are expected to begin classes this week in the 15 schools.