This quick tutorial will show you one way to create a nice and clean looking wireframe render as used in the image below.
Create a new render layer with your model selected and assign a new Lambert material to it. Set the color to black and the incandescence to white. Go to the shading group of the material and enable Contour Rendering in the mental ray folder. Change the color to black. Adjust the Width if needed. In my case 0.5 looked good.
Open the render settings and choose mental ray as the renderer. Go to the Features tab and under Contours check Enable Contour Rendering. If you want to render the wireframe as an additional render layer make sure to create a layer override first. Under Draw By Property Difference check the Around all poly faces option. Do a test rendering. You might want to adjust the Over-Sample, Filter-Type and Filter-Support Settings.
Below you can see the results with different settings.
These are the necessary steps for the basic contour rendering with mental ray. If you want to dig further into this, mental ray comes with a variety of different custom shading nodes that support enhanced contour rendering, i.e. making it possible to vary the width of the contour lines based on the angle of light or by random values to create sketch like effects. But that’s another story to be told …