by substrate you are referring to what?

imo - planting corn on any rooftop is a mistake.

if you are thinking about planting corn, on a rooftop, in 4in of soil, BIG mistake

send us pics k?

Substrate=Soil

Why do you say that corn is a big mistake, I was thinking of aiming for smaller varieties, ones growing 4 ft or so, Using some chicken wire or similar device to provide anchoring, and of course orgainicly fertilizing the heck out of it.

Possibly referring to wind damage? Hey, try it let us know how it works for you!!

Why the roof?

No deer up on the roof, plus, shingles are expensive.