OR:
Use the built in features of the Morph tool, offset does a fine job.
Note the top of wall remains flat.
When working with a curved wall, no matter if from curved wall tool
or if from polygonal wall - you must split the wall.
The offset edge command uses the center of the circle to "tilt". So
if your wall is over 180 degrees, the bottom will begin to go back up...
The advantage of this method is that the wall has a continuous slope
from top to bottom, along the length of the wall itself. Looks like the
top of wall is a spiral instead of a trimmed plane.