I have shown this in my build thread for my studio, but though it would be good to post my Ceiling Cloud build as a separate thread.
The cloud is 7ft by 11ft and I used salvaged boards for the sides which were 7 inches in width. I drilled holes through them to lighten them up and also hope to provide another way for sound to enter the insulation.
I filled them with 6in of Safe and Sound insulation.
I'm going to start on movable Gobos next so I can try out putting them in first reflection points and move them around for tracking. Holes only on the vertical sides this time...