i don't know much about Vray, but there are a couple of rendering engines that seem to do a good job.

look into Kerkythea...it's free and works seamlessly with sketchup. you will have to load on some plugins and stuff to make it happen, but the results are promising.

also, there's another one called Podium that does clay. they have a free version, but its output image is fairly small.

http://www.kerkythea.net/joomla/index.php

http://www.suplugins.com/index.php?p=page&page_id=Download

http://www.sketchupartists.org/tutorials/the-quasi-clay-style-by-oliver-shea/

the term "clay rendering" typically means a render of a scene where all the geometry has a default material applied in order to test lighting and camera views. The lack of materials enables you to focus the effects of lighting and camera view without being distracted by the effects materials/texture maps. Getting the lighting and camera views worked out first makes texturing easier and helps create a holistic and believable scene.

its done with vray dirt material, here is useful tutorial:

http://www.ronenbekerman.com/using-vraylightmtl-vraydirt-ambient-occlusion-render-checkup/

Thanks everyone. That helped alot!!

None of these suggestions are clay renders.  You're looking for a basic occlusion pass.   There are tons of tutorials online if you search for the correct term.

A clay render looks like actual clay, see Zbrush for a proper clay render.  The purpose is not to test cameras or lighting as suggested above (occlusion passes ignore lighting anyways so that point is moot), but only show a model and its details, in the most traditional sculptural sense. 

Black and white WIPs, aka occlusion passes, can be used as stated above to lock in views or take a look at the geometry of a model.  That's what you want.