Balcony is supposed to be roofless so that you enjoy the night sky having a beer, tea and relax so that you can see the moon and the stars and the cold wind. With a box-in balcony you are turning your balcony into a white elephant and i bet you will not use it. During the day you can forget about it. OUr weather is hot and even with a roof you will think of a fan unless the roof is solid roof tiles not glass or poly.

If you must have a roof, get one that is foldable one like those kopitiams fabric ones. You may not like the look compare to poly/glass.