Location of external Air con. unit on 1 st floor flat

Hello, My flat is a first & top floor 2 bedroom flat within a converted terraced house. I am thinking of installing cooling for 2-4 rooms. The house was built ~1910 and the roof is slate. The concern is that the preferred location of the external unit of a typical split system would be the rear of the house, but access to the rear for installation and maintenance would be via the ground floor neighbours flat, which makes it infeasible. The front of the house on the ground floor wouldn't be permissible, and the first floor level may be an issue with the local council/adjacent neighbours. Is there a novel solution to this dilemma? Maybe stick it on the roof? :) Thanks..