My Design prominently took the consideration of the style and function of your current build, mainly the spiral staircase, spaces and how they complement each other and looked for opportunities that can emphasize this, in a modern way, continuing its originality, flying terraces are unchanged, staircase remains, exterior and plan arrangements stay, I added a bedroom with a walk-in closet , walk-in closet for all bedrooms, a roof terrace with a jacuzzi and a swimming pool which needed a volume on a level below it, hence another floor added which also has a spacious social room, can be utilized as a study/library or a movie room (home theatre ) , and a guest bedroom with a walk in closet, a bathroom at the same location of the bathrooms below it of the current planning.
On the current layout I have added a wine cellar adjacent to the dinning room, which is next to the open kitchen, a smaller kitchen on the ground floor usable when dinning outdoors , close next to the barbecue and a ground floor sauna room, staircase enclosure is the glass curtain wall, and I have added Landscape features which are cost considerable. Hope its what you had in mind.

Thank you
Benjamin A.