The 10,500-student Mason (Ohio) district has two major construction projects totaling $35 million reaching the half-way point this winter. When they are done next summer, it will mark the end of the largest building boom in the district's history. Taking shape at Mason High School: new wings with 49 classrooms. The $30 million expansion is expected to make the high school the largest in the Cincinnati area and perhaps the largest in Ohio. On the same campus, work continues on a $5 million, two-story addition to Mason's stadium.