Pandji:
Welcome.
Make a parallel projection of JUST THE WALL with Archicad's Internal 3D Engine - hidden line version [better line quality than OpenGL.]
Use the command "Look to Perpendicular" and click on the wall face in 3D.
This will adjust your custom axonometry to render the wall orthographically.
See the attached for the command location.
You will copy this into an independent detail window in order to dimension it.
Dwight Atkinson