You will need to build a tanalised wooden frame to your existing shed roof.
How to make a sedum roof on a shed.
Remember the plants at the top of the roof will receive less water than the plants at the bottom so make sure this is taken into consideration when planting or laying sedum.
Lower the first rafter truss into place at either the front or back of the shed.
You will need two pieces of 2x4 timber the same length as the width of the roof and two pieces the same length as the depth of the roof minus 4 inches.
1 build the tanalised wooden roof frame.
Using rot proof timber build a frame around the roof to contain the garden.
Use 3 nails for each side.
Sedum plants herbs wild flowers and grasses work best as they are more resilient than most while still attracting a wide range of wildlife.
The first job is to fix an edging to the roof.
The frame can be made by simply nailing the corners together or by using l brackets to form the corners.
It will also protect it from wind uplift.
In this example i have used a pent shed roof rather than an apex which is easier to demonstrate on.
An online guide to building your own small scale green roof.
This will stop the sedum matting from drying out at the edges.
Build the frame so it provides a 3cm lip around the roof felt for the substrate and sedum blanket to be.
The diy green roof guide aims to take most of the mystery out of how to build a small scale green roof.
Line the roof of your shed with a piece of plywood wrapped in waterproof butyl lining.
Fasten the truss by driving 8d finishing nails at an angle down through the board just above the birdsmouth notch and into the underlying wall plate.
An all purpose soil less peat free potting mix is fine for growing herbs and other edibles but mix in plenty of perlite to both improve drainage and save on weight.
Lift the wooden frame into place.
This will protect the roof of the shed from any potential water damage.
Attach the end rafters to the wall plates of your shed frame.