In my “young period” as an architect I drew very precisely: my freehand drawings were also well-constructed. Then, at around fifty, my drawings became a vehicle for expressing atmosphere: the set of instinctively drawn lines and tones formed a picture and – later – a building.
As far as the concept (and the details) of a building is concerned: I have long been inventing it in my head and then explain it to those who will do the computer work.