Does anyone know the layout of the sunflower bookery?? Was it shown in the manga?
Good question. To my memory, no, the complete layout has never been shown, certainly not in anything like an explanatory schematic, as to how many rows of shelves there are and how they’re arranged, etc.
It may be the case (and would take someone with a much more developed sense of physical space than I have to determine it) that the depiction of the bookstore is consistent throughout the series so that the layout can be reconstructed, but I would note that originally the whole store was described as being inside the school grounds before being changed to in front of the school. The fact that there is a residential entrance in back of the main building is certainly a late revelation.
My impression is that we’re just supposed to get the sense of an old-fashioned Japanese building that has had a lot of additions involving many nooks and crannies.