(This site has been playing up a bit today, so don't worry if it takes a while for replies to come through.)
If your shed has enough light, you could use it to store plants, but maybe they would be better indoors if it is potted geraniums you mean.

Welcome to GoY. :-)

I think you're asking about Pelargoniums, aren't you. Some people take the plants indoors and keep them on the kitchen windowsill over the winter. You'd need to keep any rooted cuttings warm, as well.

I have had some success in shaking all the soil off and wrapping up in newspaper like fish and chips then storing in cardboard box in the shed, but if you have a good collection and dont want to risk that I would take cuttings and keep them on a landing windowsill or somewhere similar.

You are a bit late for taking cuttings - August is the usual time, but you could give it a try. Take a stem about 4 or 5 inches long and remove all but the top few leaves, and any flowers or flower buds. Let the cut surface dry (unlike most cuttings) Then pot them up round the sides of a pot of sandy gritty compost and give them hardly any water. If the stems are left in wet soil especially at this time of year they will rot. Its more like taking cactus cuttings than most plants.
You can keep the mother plants going in the house if you have enough windowsill space. The only problem with a shed is that in a cold spell it might get below freezing inside. They may survive this as long as they are quite dry so if you have nowhere else it is worth a try. I think some people suggest wrapping them in newspaper but maybe you will get some advice on this.

PS - just seen that info above this!

Hi. Just read your profile, sorry to hear your husband who used to be on here has now got ill health, (scousemonk or bigpaddy) myself I haven't talked to him on here but bet a few have, send my regards to him and hope keeps as comfortable as possible.
Goy Friend Jackie x
Oh! Good luck with your plants & garden :o))