If you had to assemble the cake on site I would make the sari ahead of time on cake dummies. This way it can try in the shape you need. The only concern is that your dummies may not be the same height as your cakes comes coated.
I personally would assemble the cake at home and attach the sari at home as well. I use stress free cake supports so I don’t really worry about the tiers falling down. Hope this helps
