Just to keep you updated, I've decided to go for a 'fleece curtain approach' to a makeshift greenhouse against the sunny side of the shed wall. As fleece is so light, I believe I will be able it peg it down along the guttering pipe with clothes pegs.
I got this idea from our neigbhour who thinks this method is even better than a conventional greenhouse with your heat & ventilation sorted yet you still get your rainwater and air through. My neighbour has implemented a similar system on one side of their greenhouse where they have a shelf leaning like a mini nursery for raising seedlings. I had thought that with my lack of experience using a greenhouse, I'm more likely to set my tomatoes on fire.
Thank you all for sharing your design ideas.