private void CreateDirectShapeFromCylinder(Document doc)
{
    // Naming convention for faces and edges: we assume that x is to the left and pointing down, y is horizontal and pointing to the right, z is up
    BRepBuilder brepBuilder = new BRepBuilder(BRepType.Solid);

    // The surfaces of the four faces.
    Frame basis = new Frame(new XYZ(50, -100, 0), new XYZ(0, 1, 0), new XYZ(-1, 0, 0), new XYZ(0, 0, 1));
    CylindricalSurface cylSurf = CylindricalSurface.Create(basis, 50);
    Plane top = Plane.CreateByNormalAndOrigin(new XYZ(0, 0, 1), new XYZ(0, 0, 100));  // normal points outside the cylinder
    Plane bottom = Plane.CreateByNormalAndOrigin(new XYZ(0, 0, 1), new XYZ(0, 0, 0)); // normal points inside the cylinder

    // Add the four faces
    BRepBuilderGeometryId frontCylFaceId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(cylSurf, null), false);
    BRepBuilderGeometryId backCylFaceId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(cylSurf, null), false);
    BRepBuilderGeometryId topFaceId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(top, null), false);
    BRepBuilderGeometryId bottomFaceId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(bottom, null), true);

    // Geometry for the four semi-circular edges and two vertical linear edges
    BRepBuilderEdgeGeometry frontEdgeBottom = BRepBuilderEdgeGeometry.Create(Arc.Create(new XYZ(0, -100, 0), new XYZ(100, -100, 0), new XYZ(50, -50, 0)));
    BRepBuilderEdgeGeometry backEdgeBottom = BRepBuilderEdgeGeometry.Create(Arc.Create(new XYZ(100, -100, 0), new XYZ(0, -100, 0), new XYZ(50, -150, 0)));

    BRepBuilderEdgeGeometry frontEdgeTop = BRepBuilderEdgeGeometry.Create(Arc.Create(new XYZ(0, -100, 100), new XYZ(100, -100, 100), new XYZ(50, -50, 100)));
    BRepBuilderEdgeGeometry backEdgeTop = BRepBuilderEdgeGeometry.Create(Arc.Create(new XYZ(0, -100, 100), new XYZ(100, -100, 100), new XYZ(50, -150, 100)));

    BRepBuilderEdgeGeometry linearEdgeFront = BRepBuilderEdgeGeometry.Create(new XYZ(100, -100, 0), new XYZ(100, -100, 100));
    BRepBuilderEdgeGeometry linearEdgeBack = BRepBuilderEdgeGeometry.Create(new XYZ(0, -100, 0), new XYZ(0, -100, 100));

    // Add the six edges
    BRepBuilderGeometryId frontEdgeBottomId = brepBuilder.AddEdge(frontEdgeBottom);
    BRepBuilderGeometryId frontEdgeTopId = brepBuilder.AddEdge(frontEdgeTop);
    BRepBuilderGeometryId linearEdgeFrontId = brepBuilder.AddEdge(linearEdgeFront);
    BRepBuilderGeometryId linearEdgeBackId = brepBuilder.AddEdge(linearEdgeBack);
    BRepBuilderGeometryId backEdgeBottomId = brepBuilder.AddEdge(backEdgeBottom);
    BRepBuilderGeometryId backEdgeTopId = brepBuilder.AddEdge(backEdgeTop);

    // Loops of the four faces
    BRepBuilderGeometryId loopId_Top = brepBuilder.AddLoop(topFaceId);
    BRepBuilderGeometryId loopId_Bottom = brepBuilder.AddLoop(bottomFaceId);
    BRepBuilderGeometryId loopId_Front = brepBuilder.AddLoop(frontCylFaceId);
    BRepBuilderGeometryId loopId_Back = brepBuilder.AddLoop(backCylFaceId);

    // Add coedges for the loop of the front face
    brepBuilder.AddCoEdge(loopId_Front, linearEdgeBackId, false);
    brepBuilder.AddCoEdge(loopId_Front, frontEdgeTopId, false);
    brepBuilder.AddCoEdge(loopId_Front, linearEdgeFrontId, true);
    brepBuilder.AddCoEdge(loopId_Front, frontEdgeBottomId, true);
    brepBuilder.FinishLoop(loopId_Front);
    brepBuilder.FinishFace(frontCylFaceId);

    // Add coedges for the loop of the back face
    brepBuilder.AddCoEdge(loopId_Back, linearEdgeBackId, true);
    brepBuilder.AddCoEdge(loopId_Back, backEdgeBottomId, true);
    brepBuilder.AddCoEdge(loopId_Back, linearEdgeFrontId, false);
    brepBuilder.AddCoEdge(loopId_Back, backEdgeTopId, true);
    brepBuilder.FinishLoop(loopId_Back);
    brepBuilder.FinishFace(backCylFaceId);

    // Add coedges for the loop of the top face
    brepBuilder.AddCoEdge(loopId_Top, backEdgeTopId, false);
    brepBuilder.AddCoEdge(loopId_Top, frontEdgeTopId, true);
    brepBuilder.FinishLoop(loopId_Top);
    brepBuilder.FinishFace(topFaceId);

    // Add coedges for the loop of the bottom face
    brepBuilder.AddCoEdge(loopId_Bottom, frontEdgeBottomId, false);
    brepBuilder.AddCoEdge(loopId_Bottom, backEdgeBottomId, false);
    brepBuilder.FinishLoop(loopId_Bottom);
    brepBuilder.FinishFace(bottomFaceId);

    brepBuilder.Finish();

    using (Transaction tr = new Transaction(doc, "Create a DirectShape"))
    {
        tr.Start();
        DirectShape ds = DirectShape.CreateElement(doc, new ElementId(BuiltInCategory.OST_GenericModel));
        ds.SetShape(brepBuilder);
        tr.Commit();
    }
}

Private Sub CreateDirectShapeFromCylinder(doc As Document)
    ' Naming convention for faces and edges: we assume that x is to the left and pointing down, y is horizontal and pointing to the right, z is up
    Dim brepBuilder As New BRepBuilder(BRepType.Solid)

    ' The surfaces of the four faces.
    Dim basis As New Frame(New XYZ(50, -100, 0), New XYZ(0, 1, 0), New XYZ(-1, 0, 0), New XYZ(0, 0, 1))
    Dim cylSurf As CylindricalSurface = CylindricalSurface.Create(basis, 50)
    Dim top As Plane = Plane.CreateByNormalAndOrigin(New XYZ(0, 0, 1), New XYZ(0, 0, 100))
    ' normal points outside the cylinder
    Dim bottom As Plane = Plane.CreateByNormalAndOrigin(New XYZ(0, 0, 1), New XYZ(0, 0, 0))
    ' normal points inside the cylinder
    ' Add the four faces
    Dim frontCylFaceId As BRepBuilderGeometryId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(cylSurf, Nothing), False)
    Dim backCylFaceId As BRepBuilderGeometryId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(cylSurf, Nothing), False)
    Dim topFaceId As BRepBuilderGeometryId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(top, Nothing), False)
    Dim bottomFaceId As BRepBuilderGeometryId = brepBuilder.AddFace(BRepBuilderSurfaceGeometry.Create(bottom, Nothing), True)

    ' Geometry for the four semi-circular edges and two vertical linear edges
    Dim frontEdgeBottom As BRepBuilderEdgeGeometry = BRepBuilderEdgeGeometry.Create(Arc.Create(New XYZ(0, -100, 0), New XYZ(100, -100, 0), New XYZ(50, -50, 0)))
    Dim backEdgeBottom As BRepBuilderEdgeGeometry = BRepBuilderEdgeGeometry.Create(Arc.Create(New XYZ(100, -100, 0), New XYZ(0, -100, 0), New XYZ(50, -150, 0)))

    Dim frontEdgeTop As BRepBuilderEdgeGeometry = BRepBuilderEdgeGeometry.Create(Arc.Create(New XYZ(0, -100, 100), New XYZ(100, -100, 100), New XYZ(50, -50, 100)))
    Dim backEdgeTop As BRepBuilderEdgeGeometry = BRepBuilderEdgeGeometry.Create(Arc.Create(New XYZ(0, -100, 100), New XYZ(100, -100, 100), New XYZ(50, -150, 100)))

    Dim linearEdgeFront As BRepBuilderEdgeGeometry = BRepBuilderEdgeGeometry.Create(New XYZ(100, -100, 0), New XYZ(100, -100, 100))
    Dim linearEdgeBack As BRepBuilderEdgeGeometry = BRepBuilderEdgeGeometry.Create(New XYZ(0, -100, 0), New XYZ(0, -100, 100))

    ' Add the six edges
    Dim frontEdgeBottomId As BRepBuilderGeometryId = brepBuilder.AddEdge(frontEdgeBottom)
    Dim frontEdgeTopId As BRepBuilderGeometryId = brepBuilder.AddEdge(frontEdgeTop)
    Dim linearEdgeFrontId As BRepBuilderGeometryId = brepBuilder.AddEdge(linearEdgeFront)
    Dim linearEdgeBackId As BRepBuilderGeometryId = brepBuilder.AddEdge(linearEdgeBack)
    Dim backEdgeBottomId As BRepBuilderGeometryId = brepBuilder.AddEdge(backEdgeBottom)
    Dim backEdgeTopId As BRepBuilderGeometryId = brepBuilder.AddEdge(backEdgeTop)

    ' Loops of the four faces
    Dim loopId_Top As BRepBuilderGeometryId = brepBuilder.AddLoop(topFaceId)
    Dim loopId_Bottom As BRepBuilderGeometryId = brepBuilder.AddLoop(bottomFaceId)
    Dim loopId_Front As BRepBuilderGeometryId = brepBuilder.AddLoop(frontCylFaceId)
    Dim loopId_Back As BRepBuilderGeometryId = brepBuilder.AddLoop(backCylFaceId)

    ' Add coedges for the loop of the front face
    brepBuilder.AddCoEdge(loopId_Front, linearEdgeBackId, False)
    brepBuilder.AddCoEdge(loopId_Front, frontEdgeTopId, False)
    brepBuilder.AddCoEdge(loopId_Front, linearEdgeFrontId, True)
    brepBuilder.AddCoEdge(loopId_Front, frontEdgeBottomId, True)
    brepBuilder.FinishLoop(loopId_Front)
    brepBuilder.FinishFace(frontCylFaceId)

    ' Add coedges for the loop of the back face
    brepBuilder.AddCoEdge(loopId_Back, linearEdgeBackId, True)
    brepBuilder.AddCoEdge(loopId_Back, backEdgeBottomId, True)
    brepBuilder.AddCoEdge(loopId_Back, linearEdgeFrontId, False)
    brepBuilder.AddCoEdge(loopId_Back, backEdgeTopId, True)
    brepBuilder.FinishLoop(loopId_Back)
    brepBuilder.FinishFace(backCylFaceId)

    ' Add coedges for the loop of the top face
    brepBuilder.AddCoEdge(loopId_Top, backEdgeTopId, False)
    brepBuilder.AddCoEdge(loopId_Top, frontEdgeTopId, True)
    brepBuilder.FinishLoop(loopId_Top)
    brepBuilder.FinishFace(topFaceId)

    ' Add coedges for the loop of the bottom face
    brepBuilder.AddCoEdge(loopId_Bottom, frontEdgeBottomId, False)
    brepBuilder.AddCoEdge(loopId_Bottom, backEdgeBottomId, False)
    brepBuilder.FinishLoop(loopId_Bottom)
    brepBuilder.FinishFace(bottomFaceId)

    brepBuilder.Finish()

    Using tr As New Transaction(doc, "Create a DirectShape")
        tr.Start()
        Dim ds As DirectShape = DirectShape.CreateElement(doc, New ElementId(BuiltInCategory.OST_GenericModel))
        ds.SetShape(brepBuilder)
        tr.Commit()
    End Using
End Sub