3 years living on the top floor of a block of flats on Peng Chau, so pretty close to Mui Wo. Spent a year on the ground floor. Two 500 square foot units. Both with a small covered portion installed by the builder, no problems during Typhoon Manghut or whatever the spelling.
Slightly hotter, I ran one wall AC unit on hot days (like window units but set in a wall opening) for cats. Probably kept 1 room around 30 every day, would switch units. Cats would hang out in the room with no AC but that room would be maybe low 30s. Only ran the bedroom unit at night.
Probably had a larger summer electric bill than I had on the ground floor but not crazy, even with leaving the AC on for the cats. Not a huge space and only one room so it was doable. Didn't have anything particularly reflective or plants because fairly hot and windy on the roof so plant maintenance is considerable and not going to water constantly, cats were enough maintenance.
Still worth it for the extra space to hang out laundry, etc. Probably could have made better use of fans and running AC units on fan only, but this worked for me. And because the flat was never allowed to get too hot, didn't take long to cool it when I returned home. Block of flats right on the sea facing Trappist Monastery.