i edited it a bit
The main part of this is choosing what each block will be. However, on large roofs, it is a good idea to make a design, like rafters, squares, etc. (insert picture of designs here) Now for the materials, my recommendation for a floor that can rarely go wrong/sideways is wood, mainly birch. It works well with most palettes, unless your using it as a wall material (I dont understand this sentence fully), Different types of wood also look great with different palettes. Also, make sure your roof or floor isn't the same material as your walls.
Carpet is also an option, however(,) I don't recommend bright colors, unless it's a themed room, then you can sometimes get away with it. I also recommend to avoid stone, the only place that should have pure (you dont need pure) stone is the garage, a place where a concrete floor makes sense (a concrete floor also makes sense (?) ). Also, don't mix floor designs, try to keep it all the same, except for kitchen(s) and bathrooms, for those tile floors work well.
Double-thick floor/ceiling is a nice addition (i dont get this), however you need to plan that during the exterior building stage (Windows might not be even on each floor (i think this is out of context?) ). If you don't have it (any windows) however don't worry, you can get along fine without it. Another nice feature that has to do with size is having each floor (room) 5 or 6 blocks tall. This gives a nice amount of space to add a rim to the ceiling and more freedom with the lighting. At first this might sound like a lot, but after trying it you will like it more, I know from personal experience. However, if you can't do this, I recommend 4 blocks as a minimum.
