These are the edges which make the vertical faces of the solid. From the sorted groups, pull the item at index 1.Group the edges (step 5) by the Z values, and sort the groups by the unique keys (List.GroupByKey and List.SortByKey - I believe you’ll want and for the inputs to sort by key, but I may be mistaken).Pull the point at parameter 0.5, and quarry the Z value (Curve.PointAtParameter, Point.Z). Convert the edges to curves (Edge.CurveGeometry).Pull the edges (Topography.Edges) of the solid.

Thicken the surface in one direction (Surface.Thicken).

If step 5 is too difficult, you could go another route: You may need to utilize two of them in sequence, one with the RightSide input set to true and the other set to false.

Use a Polycurve.Fillet node to fillet the surfaces.

Group the curves into curve loops (Archilab’s GroupCurves node works well, if you can’t use that you can search the forum for ‘group curves’ as there are several solutions for this), and build a polycurve of each group.At this point the curves where the roadways cross will be trimmed, but you won’t yet be filleted. Pull the perimeter curves of the surface.Combine the surfaces into a single surface with a Surface.ByUnion node.Patch those curves into a surface with a Surface.ByPatch node.Instead of offsetting the curve, use a Polycurve.ByThickeningCurveRadius node.

This assumes your initial centerlines are planar.

City revit