Much like another question I am trying to create a ceiling. I was wondering if one can use the raise/lower height terrain brush function on other 3d objects such as a plane. I am wanting it to appear that the ceiling/sky is melting, I am not interested in having it animated just the peaks coming down from the top. Cheers :0)
You could just create a terrain and then flip it.
The work around I have come to is create the terrain you want as your ceiling, export as raw, open it in a 3d editor then export it to a file supported by unity.
I followed this wonderful tutorial, it didn’t get quite the effect I wanted but I’me running short for time 
