partial class Examples
{
  public static Rhino.Commands.Result AddCone(Rhino.RhinoDoc doc)
  {
    Rhino.Geometry.Plane plane = Rhino.Geometry.Plane.WorldXY;
    const double height = 10;
    const double radius = 5;
    Rhino.Geometry.Cone cone = new Rhino.Geometry.Cone(plane, height, radius);
    if (cone.IsValid)
    {
      const bool cap_bottom = true;
      Rhino.Geometry.Brep cone_brep = cone.ToBrep(cap_bottom);
      if (cone_brep!=null)
      {
        doc.Objects.AddBrep(cone_brep);
        doc.Views.Redraw();
      }
    }
    return Rhino.Commands.Result.Success;
  }
}

import Rhino
import scriptcontext

def AddCone():
    plane = Rhino.Geometry.Plane.WorldXY
    height = 10
    radius = 5
    cone = Rhino.Geometry.Cone(plane, height, radius)
    if cone.IsValid:
        cap_bottom = True
        cone_brep = cone.ToBrep(cap_bottom)
        if cone_brep:
            scriptcontext.doc.Objects.AddBrep(cone_brep)
            scriptcontext.doc.Views.Redraw()
    return Rhino.Commands.Result.Success

if __name__=="__main__":
    AddCone()