Here is the full code for the edit profile of an extrude feature example from the API documentation.
Look under the "create base extrusion 4cm thick" comment.
You can see how the extrusion is made.
Just replace the kJoinOperation line with kNewBodyOperation for Inventor to create a new body.
Public Sub EditFeatureProfile()
' Create a new part document, using the default part template.
Dim oPartDoc As PartDocument
Set oPartDoc = ThisApplication.Documents.Add(kPartDocumentObject, _
ThisApplication.FileManager.GetTemplateFile(kPartDocumentObject))
' Set a reference to the component definition.
Dim oCompDef As PartComponentDefinition
Set oCompDef = oPartDoc.ComponentDefinition
' Create a new sketch on the X-Y work plane.
Dim oSketch As PlanarSketch
Set oSketch = oCompDef.Sketches.Add(oCompDef.WorkPlanes(3))
' Set a reference to the transient geometry object.
Dim oTransGeom As TransientGeometry
Set oTransGeom = ThisApplication.TransientGeometry
Dim oCenter As Point2d
Set oCenter = oTransGeom.CreatePoint2d(-5, 0)
' Create a sketch circle
Dim oCircle As SketchCircle
Set oCircle = oSketch.SketchCircles.AddByCenterRadius(oCenter, 1)
' Create a profile based on the circle
Dim oProfile As Profile
Set oProfile = oSketch.Profiles.AddForSolid
' Create a base extrusion 4 cm thick.
Dim oExtrudeDef As ExtrudeDefinition
Set oExtrudeDef = oCompDef.Features.ExtrudeFeatures.CreateExtrudeDefinition(oProfile, kJoinOperation)
Call oExtrudeDef.SetDistanceExtent(4, kPositiveExtentDirection)
Dim oExtrude As ExtrudeFeature
Set oExtrude = oCompDef.Features.ExtrudeFeatures.Add(oExtrudeDef)
' Draw a 4cm x 3cm rectangle with the corner at (0,0)
Dim oRectangleLines As SketchEntitiesEnumerator
Set oRectangleLines = oSketch.SketchLines.AddAsTwoPointRectangle( _
oTransGeom.CreatePoint2d(0, 0), _
oTransGeom.CreatePoint2d(4, 3))
' Add all the lines of the rectangle to an ObjectCollection
Dim oPathSegments As ObjectCollection
Set oPathSegments = ThisApplication.TransientObjects.CreateObjectCollection
Dim oEntity As SketchEntity
For Each oEntity In oRectangleLines
oPathSegments.Add oEntity
Next
' Create a profile that represents the newly created rectangle
' and excludes the original circle.
Set oProfile = oSketch.Profiles.AddForSolid(False, oPathSegments)
' Set the new profile
oExtrude.Definition.Profile = oProfile
End Sub
