Well, you need a real life example. The best example is actually the old world trade centre because it was a straight block. So the top floors should be wider than the bottom ones on a round earth.
The towers were 1368ft and 1362ft. Ok, we'll pick the taller of the two and wikipedia tells me its top floor was at 1347ft

The floor plane is as so.

The radius of earth is 2.0891×10
7 feet. (20,891,000)
So to the base we have an isosceles triangle of 20,891,000 feet for two sides and 208 for the top edge. With some basic trig I calculate that the width of the top floor therefore needs to be 208.0077280857326 ft.
So the top floor is 43267.21494338807069 sqft
and the bottom floor is 43264 sqft
So the top floor of the world trade centre had an extra 3 square feet than the bottom one! Space for a toilet, or a printer cupboard or something. Round earthers just ignore these things as if no one would notice. The building actually has 165 sqft more to offer than advertised in each tower. That's a few extra offices! And no one noticed?
Round earthers are playing for ignorance again.