Carport greening in existing buildings: weight and materials

Hello, I am interested in the extensive greening of a large approximately (11m x 6m) 4-car carport with as little weight as possible. The carport already has a root-resistant covering with Firestone Rubbergard EPDM.

Does anyone have experience with one of the following techniques/configurations?

1. Knauf Urbanscape
2. Nophadrain

Urbanscape recommends a gravel edge around the greened area (with Nophadrain it will probably be similar). This significantly increases the weight. Therefore:

Could the drainage gravel be replaced with foam glass gravel? Is there any objection to this?

What else should be considered?

Thanks in advance