In 3D industry, 3D model designers rendered their model with the wire frame for the presentation or behind scene of the movie, so audience can see the topology of the model while looking at the detail of the model. If you are using Maya for the 3D modeling and animation you can use contours rendering in mental ray. Now lets see how to render your scene with wire frame.
First open your scene and select the object that you want render with wire frame. Go to attributes editor and then to shading group properties(click on the arrow icon next to the material name or select the shading group in hypershade). Scroll down to mental ray section. There you can find contours settings. Check on Enable Contour Rendering. Then set the color to black. Width of a line will be depend on your scene scale.
Then go to render settings window. Switch to Features tab. Expand the contours section. Check on Enable Contour Rendering. Set over-sample to 3 and Filter type to Gaussian Filter. Finally check on Around all poly faces under Draw By Property Difference section. Now you are ready to go.
You can use any material for contour rendering. Make sure that you are using production settings in mental ray for quality wire frame.