To Construct a Thin Shelled Solid with an Open Face

Select the Thin Shell Feature tool.
The Thin Shell Feature tool settings window opens.
Key in the Shell Thickness value.
In the Face Thickness field, key in a value of 0 (zero).
Select the solid.
Select the face to remove.
(Optional) Select additional faces for removal with <Ctrl> + Data points.
Accept or reject the thin shell construction.

Top: Original geometry. Select the solid (1), then select the face with a value of 0 (2). Left: Side view of shelled geometry. Lower Right: Isometric view of shelled geometry.