-
Here's the guide I used:
https://www.fixmyroof.co.uk/how-to-felt-a-shed-roof/#
You can get different colours. I wanted green, but black/grey was cheapest*. Mine was seconds mineral torch-on stuff from ebay/some guys garden. One end was a bit knackered from being stood up on its end and another section was creased, but I just positioned it so those bits got trimmed off. Collecting was a bit more faff but it still cost the same/less than the thin shed stuff from Wickes.
But if I were you I'd throw on some cut up blue Ikea bags as an incentive to complete the living roof....
... although you could always put the living roof on top (pending weight restrictions).
*and matched the other sheds, preventing mission creep and wrath from Mrs. H. who already thinks 3 sheds and a brick outhouse is too much
I may chuck a load on the top as soon as I finish the roof - that way, I don't need to complete the live roof straight away, and have more time for dithering.