Can you be more specific about what problem you are trying to work out?
Generally class B generally means townhouses where the strata are arranged side by side and the unit owner has responsibility to repair and maintain anything on the unit area. There are exceptions set out in the Unit Title (Management) Act allowing an Owners Corporation to resolve to take over certain maintenance responsibilities, for example, so that the OC does all the exterior painting at once.
Class A generally means apartment blocks where the strata are arranged one above another. In class A the building structure is generally common property because it holds up and puts a roof over multiple units. In class B the walls and roof generally only serve one unit, unless it’s a party wall shared with another unit and with the boundary through the centre line of the wall.