3d modeling (CNC carving)

I need someone to help me model in 3D a piece for CNC carving. The model should be exportable for 3-Axis CNC carving on MDF. The dimensions of the whole piece should be 21 inches width x 7 inches depth x 3 inches height. The geometry of the modeled texture can be stretched to fit the specified dimensions The model should be exported to a format compatible with Rhino.(step file)