This example adds a rounded rectangle to slide one in the active presentation. The rectangle has the same dimensions as the text bounding box for shape one.
With Application.ActivePresentation.Slides(1).Shapes
Set tr = .Item(1).TextFrame.TextRange
Set roundRect = .AddShape(msoShapeRoundedRectangle, _
tr.BoundLeft, tr.BoundTop, tr.BoundWidth, tr.BoundHeight)
End With
With roundRect.Fill
.ForeColor.RGB = RGB(255, 0, 128)
.Transparency = 0.75
End With