Growbags

This company is exploring the possibilities for growing in modular bags, creating an extended container garden that can be used to create green roofs as well as on the ground:
http://www.pockethabitat.co.uk/

It's been used here to green a concrete space very effectively.

made from recycled polypropylene, a good take on the growbag idea.

Another idea; Public Farm One, was picked by the MOMA in New York to be constructed in 2008. Whilst it looks more permanent, it is actually built from cardboard tubes. Designed by Work Architecture Company, the green roof of fruit, vegetable and herb plants shelters a farmers market, a kids grotto, benches, swings and a pool, and the supporting columns provide solar energy outlets for charging electronic devices, and inbuilt speakers create different 'sound environments'.

http://www.publicfarm1.org/index.php?/ongoing/about/