I am going to answer from a scientific viewpoint, and away from the 'eww' factor that often pervades advice websites.
Many cockroaches are detritivores, which according to the Harvard Library website Cockroaches, they
live on decaying vegetation and the like. They can play an important role in breaking down decomposing organic matter and cleaning the environment.
There are some websites and groups that advocate keeping and even breeding cockroaches for composting, such as the Unconventional Farmer Cockroach Composting page, which state, in terms of compost benefits,
Eliminate waste efficiently (produce few nutrient dense droppings per large food intake)
Also, if they are in your compost they are happy - a warm moist environment with plenty of food. They are very unlikely to venture into the house. According to the World Health Organisation document Cockroaches, even though they are not considered to be a primary source of disease, they can spread intestinal diseases, such as
diarrhoea, dysentery, typhoid fever and cholera.
the WHO also states that the key to control is cleanliness, deny them a food source anywhere but their happy compost home and they would have no reason to venture from the compost.
Whether or not they are a pest depends on their species, according to Johnson Group Pest Control page (the page is included as it includes images as part of the descriptions),
Common types of cockroaches in Hong Kong include Periplaneta americana (American cockroach), Periplaneta australiasiae (Australian cockroach) and Blattella germanica (German cockroach). Of these three species, the one that has the greatest potential for becoming persistent and troublesome is the German cockroach, which prefers indoor locations.
If they are on the roof, it may be an option to have the air ducts etc checked for other nests within the building.