The garden is about 500 sqf (50m2) with about 10 inches (20-25cm) of earth and, below that, there's about 6 inches (15cm) of large pebbles for draining covered with a layer of felt.
The greenhouse is about 100 sqf (9m2)
I'm planning to read as much as possible about permaculture next winter, but before that, I would love to hear a general idea of what the pros would favor in terms of plants and design in such conditions, just a general spontaneous idea.
There won't be much legal constraints as the place belongs to the family.
This is the climate https://en.wikipedia.org/wiki/Lausanne#Climate Elevation is 1220 ft (372m)
South facing, but the building starts casting its shadow from about mid-afternoon.
First off - what do you want from the space? Food growing is a given, but I assume you want it to look lovely as well both for yourself and from the neighbouring buildings So make a list of things you would like to use it for - you might want a space for entertaining for instance, but if you don't then you could build more raised beds around the edge of the terrace - where the pots are now for instance.
Planting - It's hard to tell from the photos how long those beds are, or where the windows look out onto, but I would say you have room for more than one tree Choose things on dwarfing rootstocks as there's not a great depth of soil. Having decided where your tree(s) will go, add some fruit bushes - group them together so it looks natural. The rest of the space can then be filled with perennial or annual veggies, herbs and flowers. Think about what you like to eat, and for flowers, choose things that are easy to maintain and if they seed themselves around are easy to pull out.
You might also want space for (eg) compost bins.... with that depth of soil, you will need to add a nourishing mulch every year.
The greenhouse is big! Set aside some space for raising seedlings etc, but you could also have raised beds in there. I assume the roof can take the extra loading - usually with roof gardens raised beds (the weight) is arranged round the edge of the roof, but here they are more central, so I'm assuming the roof is capable of taking the weight. If you're not sure please check!!
If there's a view you want to screen (all looks beautiful in the pic, but you never know) have climbing plants growing up a trellis by the edge of the terrace.
There is a fabulous permaculture roof garden in Bristol, UK. If I can find it I will post a link. That might also give you some inspiration
I assume a mixture of food growing and supporting plants.. for the food growing plants always look at what you actually eat, and what is expensive or difficult to get hold of? For example I always grow tomatillos- you can't buy them in shops here, so I grow my own.