Section Detail for 2nd floor Sunroom

We are designing a 2 level sunroom (16" floor elevation Diff) on the 2nd floor of our house (presently a bungalow).

The lower level being 7ft wide and 25ft long will be filled by about 12" of soil to grow small plants, herbs and vegetables. This area will be sloped towards a gutter which in turn is sloped towards a retention tank. the floor system is wood construction and I am looking for products that will not infuse chemical into the soil or roots.

from what I have gathered, the section detail should be as follow:

1. Growing medium: Soil

2. Filter membrane: Geotextile

3. Root barrier: I have seen a lot of products but none that clearly say no contamination of soil (as they all are infused with chemicals)

4. Drainage layer: something that will not get crushed over the weight of the soil and plants and us walking on the soil with 10 to 15 yrs lifespan.

5. waterproof membrane: should I use roofing material (1 ply or 2 ply membrane), liner material (shower liner) or M3/Blue skin products?

and lastly should I install another material between layer 5 and my subfloor (3/4" plywood) such as rigid insulation or other material?