Positioning the wall panels
Note that the wall-panels for the front and rear frames do not sit flush with the sides of the frames.
They are in from the sides 2 1/4" (63mm),
which is the thickness of a frame member plus the thickness of the plywood.
When you lay the front and rear wall frames on a flat surface in readiness for the panels, pencil a line down each side of each frame,
2 1/4" (63mm) in from the edge.
That will give you a line to align the wall-panels to.
In other words, the panels will be off-set 2 1/4" (63mm) in from the side edges of the frame.
Cutting away the door-fame bottom plate
Cut out the bottom plate in the doorway and replace it with a temporary brace fixed to the underside of the plate, each side of the doorway,
so the frame cannot spread out or close in until such time as it is ready to be securely fixed in place.
Wall panel nailing detail
Nail the sheets to the frame members with 2 1/2" (60mm) galvanized flathead nails spaced at a maximum of 6" (150mm).