A living roof is a roof covered with vegetation. It provides many advantages, including improved air quality in urban centers, aesthetics, insulation, and vegetation/habitat for small animals. In 2017, I installed a living roof over my potting shed. This is how I did it:
I built rafters at a 12-inch spacing on ¾ inch MDF, strong to handle snow load. I built a frame around the roof, for a 3.5-inch soil depth. I used pond liner to prevent leaking. The edge of the roof space was lined with shingles. We ran vinyl deer fencing long ways between layers of soil, and we were ready to fill and plant. I made my own mix of soil to keep it light and well draining - a mixture of coconut peat, vermiculite, perlite, and utilite. The plants took off! They still have a long way to cover the entire roof space but it was clear they loved the space. The birds and bugs quickly started to use the space. Plants cool themselves much as we do. During hot summer days, you can feel the inside of the roof is far cooler than the outside temperature.