You are not able to place sloping columns on a
work plane, you could do that for beams after
they are created
structural columns that are slanted
are rotated WHEN BUILT BY REVIT
such that their local xy axis is oriented vertical
so if you look top down webs are vertical as shown in image
and the cross section rotation starts out at “0”
(just like in your image when you look top down on your structural columns in Revit are they also oriented web vertical)
this is the same for beams and is typical of most BIM software including
structural analysis software…
are you trying to rotate the columns such that the ends are pointing in a certain direction?
if so…then
say you wanted to orient the columns in the EAST WEST Direction
then you could find the best fit plane for each column and find the angle
between that and the EAST WEST plane and then change the cross section rotation as shown
Note that Revit is touchy so if the columns are pointing in a neg direction you may need to
adjust the angle. This is similar to this example Place Beam three dimensional in family or project with orientation - #3 by msgambelluri
good luck. here is the gh script
Also note that this is only ONE way to attack this problem both on how to correct Revit cross section
rotation and the components used in the GH image