I didn't use Devore, but another black velvet that was almost as good, so can't say for sure how the Devore would fare on the ceiling, but I would think that if you stretch and staple it to a frame as I did, it shouldn't sag.
I used black plasterboard screws to hold the ceiling frames in place, and velcro for the soffit frames. You can see the screws if you know where to look, but you can get velcro 'buttons' that can act as screw caps. They're not as black as the velvet, but work well enough to be invisible during a movie, which was all I was really concerned about.
Pics are difficult as everything is black and very little light, but if I remember, I'll see what I can do.