ATLANTA — Cortland Partners has begun building Avalon Ridge Apartments in South Atlanta. Located at 183 Mt. Zion Rd., the $26.6 million mixed-income community will have 222 one-, two- and three-bedroom apartments. The first residents are expected to move in next summer, with full completion the following winter. Amenities will include a park-like central courtyard with a swimming pool, a playground and picnic areas.