I like making green roofs but one problem with them is that I nearly always build on extensions and garden buildings at the back of houses so no one but the home owner gets to see it. Bike sheds are usually at the front of the house so they are on show to the world.
This one I built in Dulwich, London is for a client I built a sedum roof for last year. I persuaded them that this one would look nicer with a wider range of plants. I put in a selection of sedums including Sempervivum for long term coverage and then added herbs: creeping thyme, chamomile and rosemary. Then I added some saxifraga and a selection of plants that are flowering now for cover.
Green roof in Dulwich 
Flowers growing in East Dulwich 
Bike shed in East Dulwich 
Japanese maple in the foreground 
Growing like crazy 
Sedum in the foreground 
Growing well 
Overhang 
Flowers on a bike shed 
Spreading over the whole roof 
Some height but not too much 
Responding well to the rain 
Starting to spread 
This will spread and replace the pansies when they die out
I think you will agree it looks fantastic now. If you want one for your bike shed get in touch. alex@ecoalex.com