If the goal of a folding wall is both visual AND sound separation, pay special attention to wall rating, seals and provide a sound barrier above the ceiling. Creating the barrier with drywall, while possible, rarely works as intended. Fixing a sound problem later is often imperfect because it is just too complicated.

Lead sheet is the ideal material for blocking sound because it is dense and flexible for an airtight fit around penetrations and the perimeter of the ceiling plenum. Lead is not a good idea any more for environmental reasons. The material we have used as a replacement is:
SoundBlocker1™  - Reinforced Flexible Sound Barrier
See http://www.gretchken.com/

Avoid duct penetrations and use dampening in ducts that connect to spaces you want to isolate.

Be sure to inspect the work before subcontractor leaves. Test by clapping or loud music to see if it is satisfactory.