A major feature of Handset Designer is its integration with AutoCAD drawings. You can obtain an AutoCAD drawing for your project and easily import it. Also, you can draw a building in AutoCAD, then import the drawing into Handset Designer.
Further Reading
For more information on the integration between AutoCAD and Visio, visit http://office.microsoft.com/en-us/visio-help/open-insert-convert-and-save-dwg-and-dxf-autocad-drawings-HA102749361.aspx?CTT=1