There are several different approaches you can take.
You can use civil cells, you can model the bulk of the roundabout as a roadway with templates, you can model using features and surfaces.
There was a Coffee Corner presentation on this sort of thing last month.
And I believe there are lessons on roundabout modeling on the Bentley Learn Server.
MaryB
Power GeoPak 08.11.09.918Power InRoads 08.11.09.918OpenRoads Designer 2021 R2