I don't understand your question Vicki. An unheated greenhouse is just a room. You can make a solarium I suppose.

Yea, there are, but quite often, books on greenhouse growing also include information on heating and growing with heat. It might be better to go and have a browse at greenhouse growing books to make sure the one you get covers unheated greenhouses. I know Alan Titchmarsh has a Greenhouse Gardening book, but I'm not sure whether it covers unheated greenhouses specifically. Some titles for greenhouse gardening in the link below.

http://shop.rhsshop.co.uk/shop/Greenhouse-Books

This article might be of interest though, despite its age - an unheated greenhouse might not be warm enough for anything during winter if you're in a cold region, so the further north north/east you are, the more likely that is to be true - unless you're near the sea

https://www.independent.co.uk/property/gardening/cold-its-freezing-1568001.html

It'll come into it's own if you put plants in pots in there in early Spring? Earlier seed germination than outside, better environment for cuttings, etc.
It's just a little milder than outside which can be a nice advantage that's fairly significant if you're a nerdy gardener...

The Arboretum at Flagstaff probably has some information and suggestions. They have been experimenting with passive solar greenhouses for many years. I believe that the TV show "Growing a Greener World" has an episode about year-round gardening in them.

Looking for gardening podcasts I also came across passive solar greenhouses. Looks interesting!