1. To stop your shed from penetrating moisture, first you need to line the roof. Carefully cut the top of your compost bag and empty out the soil for later. Then make a plastic sheet from the bag by slitting the side seam. Use it to cover the shed roof, making sure there is a slight overhang all the way round. You may need more bags depending on the roof size. If so, make sure the highest bags are layered on top to enable drainage. Tack the overhang all around the shed roof frame with the roofing tacks, approximately every 20cm.

2. Starting at the front (lowest side of the roof), measure then cut a length from a decking board to fit. Holding it against the shed, pre-drill pilot holes which will go through both the decking board and also into the roof frame of the shed. The holes should be approx 15cm apart and drilled into the bottom third of the board to make it stable. Using exterior wood screws, screw into place. Repeat on the opposite (highest) end. Then each of the two sides. When all four are in place, drill 2cm diameter holes at the lowest end (approx 15cm apart) to help drainage.

3. To add strength to the structure, insert a small block of wood in each corner, and using a drill, again make pilot holes that go through the blocks and into the new frame. Hold into place with exterior wood screws.

4. To improve drainage, pour a layer of gravel (2-3cm deep) into the frame — you could also use stone chippings from your driveway or any small stones you might find out on a walk. This will help to aerate plants.

5. Prevent the compost sinking into the gravel by cutting an old sheet or duvet cover to size and lay it inside the frame. This will also help to stop weeds.

6. Fill your frame with the multi-purpose compost — mix with any leftover gravel for added drainage. Bark chippings will also work if you have any in your garden. If your shed is old and can’t take the weight of the soil, place potted plants on the gravel instead and surround with bark chippings.

Drought and wind-resistant species work best. Go-to green-roof plants include sedums and succulents, but it’s worth experimenting with grasses such as Stipa. Herbs like oregano work well, and low-growing flowers like saxifrages are great for attracting insects and butterfies. To keep your roof well-maintained, only water in dry periods, as saturated green roofs can add unnecessary strain to the structure. Remove unwanted weeds and check drainage holes are not blocked. Retreat the wood every autumn by brushing wood preserve onto the wooden structure. Sprinkle a handful of compost around each plant in late winter/early spring to boost nutrient levels.