My mom would sure love the idea !

she does have made some plants garden on top of the roof .While it was an interesting story though ,the lady who brought some plant seeds was not able to grow any in her roof top while she gave some to my mom and after few days they were grown in our roof top & now she has grown Potato, coriander,some vegetables that I do not know the names of ;)

I an thinking of making a post with those plants of hers ;)

All the very best to the plants growing out of them I do like the idea of yours !