This one should be easy to implement as the game already has a function that can change the view based on height (slice tool). I would like to fine tune that tool so that it makes it easier to view inside a building and place furniture.
Currently it is possible to place furniture in different floors but it can be tricky because you have to approach it from almost eye level. If by using the slice tool you can view your building floor by floor it would allow for a cleaner placement of furniture and additional building (should you need to remodel). This suggestion has been somewhat made before, but no solution was offered so I made this post. If you wish view the post made by Phagocytosis you can do so here:
If you just want to see a visual of the issue Phagocytosis made a recording of it and placed it on youtube. To save you time you can skip to 3:15 in the video when he starts building to see this issue.