Our winter garden is indoors
We had a winter garden built on to our house as an additional room, without heating or air conditioning. It has lots of windows, mostly facing the street (South-Southeast). We hired an architect who was interested in environmentally-friendly architecture. His biggest mistake was to specify wood doors and windows. Mildew has been a big problem; metal would have been better. After the contractor was finished, we did the tile floor, which has a drain to the driveway outside, and a planter bed. We put a pond liner in the planter bed and filled it with soil, except for space for an approx. 40 gal indoor pond from Walmart, home to 3 6-year old goldfish.
The plants in the winter garden include, but are not limited to, hibiscus, a fig tree, a purple-leaved pond taro, lots of asparagus fern, lantana, many amarylis, scented geraniums, jade plants, etc. etc. When the danger of frost (and, we learned last year when we lost our fig crop), cold north winds is over, almost all plants go outdoors. The fig, and the other largest pots, go on a deck just outside the winter garden. The amarylis, hibiscus, and most other plants, go out in their pots, dug into the soil. Some years a tree frog takes up residence in a pot outdoors and comes into the winter garden -- with the pot -- where she or he seems to survive quite well without any additional care from us. Seeing a tree frog inside one's house is a novel experience.
For designing the winter garden (actually Wintergarten) we had some German books.
We love it because we can have large, non-frost hardy plants, in our summer garden. And a few fresh figs, almost impossible to buy here, and when available, very expensive.