Several folks on Hometalk have posted on those, Elisa, including these at a school:
You can use the search box at the top of the page to find other examples.
are you asking about rain gardens...or growing plants in a gutter?
I tried strawberries in rain gutters. It did not work for me here in IN. I could not keep them watered enough...dried out very quickly...like in hours on a hot day.
No gardens, but the squirrels and coons kept destroying my bird feeders so we attached old gutters to the outside rail of the deck and everyone is happy