Welcome to the Vine Peppa. I'm not sure what you are planning. Rat certainly knows what he is talking about - BUT - where are you in the country ? If you go into your personal profile you can let us all know.
How hot will it be in that shed with a clear roof. It might work if you want to start things very early in the year. By now it gets very hot - I'm finding the conservatory is too hot for seedlings.
Think about what you want to grow and how early you want to start them - and where you will put them after they have germinated. Sorry, I think I have given you more questions than answers. Maybe other Grapes have more experience, or suggestions for tis one.

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