Greenhouse or potting shed?
I am in the very fortunate position of having a conservatory, a very large shed and a small 6x8 greenhouse, which I only acquired 2 years ago as an offer on our local freebie web site.
I would say greenhouse every time. Note. Try to acquire a much bigger greenhouse than you think you need. You will always need a bigger size than you buy. 10x12ft would be my ideal starting size.
I bought a staging unit which this year I moved outside, put it on the North side of the greenhouse to take potted treasures while the weather was good. Just waiting for the tomatoes to finish before moving it back inside the greenhouse for the winter.
I also love working in the greenhouse in bad weather, even just sitting on the cat's chair with a cup of coffee while the rain hammers down and the wind whistles outside. There is something comforting about "just sitting" with your plants, feeling cosy.
Incidently, I have used unused white terylene lace curtains as shading both years. Works really. Have just taken them down, whizzed them through the washing machine and put them away until next year. I have enough curtaining to drape down both sides, over the top and one end, leaving only the North end uncovered where the door is. When they start falling apart I will start hunting in charity shops for replacements.
edited October 2020
I have a 6x8 greenhouse that I wouldn't be without. 10x12 would be nicer but a tighter squeeze in my garden.
It's currently full of Brugs, cuttings and Agaves. Soon I'll have to find room for Cannas, Sweet Pea & Nigella seedlings.
I can barely open the door after that, never mind sit it. Sadly.