First, how many floors is between the “bottom” of the building and the “top” of the building??
Second, there should be an existing path for physical wires to get to the top floor as there are has to be connection to the basement usually to all floors. For instance, are there any phone lines on the top floor? IF so, they have to be connected to the phone company demarc, usually in the bottom floor or basement. Also, electricity and heating/cooling controls have to be ran from each floor to the basement/bottom floor.
So, my suggestion would be to have switches on each floor and connect them together physically and then trunk those 2 switches to one router.