Would be good to know which ARCHICAD version you are using, but generally, you can do this in the last several versions for sure.
In the "Floor Plan and Section" panel of the Roof Settings Dialog, there are Pen and Line Type settings for both Uncut Lines (lines below the Floor Plan Cut Plane) and Overhead Lines. But for Overhead Line Type and Pen settings fields to be displayed in the Settings Dialog, make sure that the "Floor Plan Display" field is set to either "Projected with Overhead" or "Overhead All".
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