I followed the tip for creating an inclined roof with windows, and used the rotate about horizontal axis after importing the wall to set the angle. When I add a beam, drawn as a box, and rotate it about the same axis by the same angle it does not match the angle of the roof! I have to add 10 degrees ...

I need to put a ceiling beam into a model, which would be easy if I could set an elevation for a wall, but I don't see any way of doing this. Looking for suggestions. Thanks in advance.
SiriJodha