Here's a recent project I created at NineteenTwenty. I helped with the clouds in the opening shot. Created in Houdini from a pretty comprehensive set of custom tools I worked on, which helped get the correct look of shapes and types. I created a mini library of Cumulus, Cirrus, and various trailing clouds. Shot was rendered in Mantra.
I also lit and rendered the opening of the roof, also rendered in Mantra.