Explanation:
how tall is the building with 9 floors now ?
or how high or tall is ombre floor ?
you left out crucial information.
I can give you only a relative answer assuming that the autumnal floors would have the same heir as the existing ones :
the existing building with 9 floors has a ratio of 9/9 floors, so it's size is 9/9 = 1/1 to its current size.
the extended building with 15 floors would have a size of 15/9 = 5/3 times its current size.