Posted: 25/08/2017 at 09:25
Thanks for all the idea and information.
The building is a self built summer house, the roof gradient is very slight and the roof is held up buy 22 6x2inch wood joists spaced 26cm apart. Over the wooden joists there is chipboard, then a thick pond liner.
There would be a lip around the hole roof with a gravel boarder for drainage. I also think the trays will keep the weight down as there will be a lot of air space underneath them.
I was thinking I would put a root barrier down followed buy the trays, each tray would have a light soil mix to keep the weight down.
I really like the idea of chicken wire to hold the trays down.
I want to grow wild flowers in the trays.