In the city, people claim a green roof will save energy, reduce the heat island effect, and prevent stormwater from overflowing the sewers.
A cabin in the woods doesn't have the second two problems, and I doubt there would be enough energy savings to justify the expense, so there is no real reason to install a green roof unless you want a real expensive squirrel feeder.
I don't know how much green roofs cost in your area, but people are paying $15 to $20 per sq. ft. for them in NYC. Then they have to irrigate them for two years until the plants are established.
Install a heavily insulated conventional roof instead
Rather than planting a green roof, I would install a conventional roof with plenty of insulation.
- Use two inches of rigid foam on the roof deck, then spray the underside with expanding foam.
- The most environmentally preferable roofing option is a standing-seam metal roof. They last 25-plus years, and have no petrochemicals as asphalt roofs do.
If you don't like the look of a stainless-steel roof on a log cabin, I wouldn't have a problem recommending a small, cabin-size asphalt roof-as long as you take advantage of the renovation and beef up the insulation in your walls, too.
- Closed-cell spray foam or blown-in cellulose will make your cabin extremely energy efficient, and cozy in the winter.
- I realize this is a lot of plastic for a cabin in the woods, but if you burn less carbon to heat the place than you otherwise would, maybe the earth will forgive you for using a few asphalt shingles and some plastic foam.
Supporting native plants
If your aim is to save water and encourage local biodiversity, there are other ways to achieve this.
- Install a rainwater catchment barrel connected to drip irrigation so you don't have to water your yard as much.
- Maybe you have a local nursery that can recommend native plants and flowers for landscaping.
If you dig up the invasives that are already there, chances are native plants will grow back naturally.