1. Build a 2 × 4 stud wall that is 4 ft. wider than the planned wall opening and 1 3/4", shorter than the distance from floor to ceiling.

2. Raise the stud wall up and position it 3 ft. from the wall, centered on the planned rough opening.

3. Slide a 2 × 4 top plate between temporary wall and ceiling. Check to make sure wall is plumb, then drive shims under the top plate at 12" intervals until the wall is wedged tightly in place.