Paint walls, doors and furniture on a grid, floor by floor, and get the block list.
Walls are counted × wall height; floors, doors, windows and furniture count once. Windows replace one wall block per row of the wall height. Save the .json to keep working later.
Sketch a base before you break ground. Paint walls, windows, doors, stairs, floors and furniture symbols on a grid with paint, rectangle, fill and flood tools; add labels for rooms; add floors that show the floor below as a ghost. The materials panel counts walls times your wall height plus everything else, and the plan saves as a .json you can reopen later or as a PNG for your build notes.
Add a floor above and paint the roof outline one block in from the walls per level — the ghost of the floor below makes stepping it in easy.