Here lies one of the greatest grey areas I have ever come across in all my years in the building industry, leading to many disputes between home owners, builders ,kitchen companies and the retail outlets.
It usually will always come down to cost and lack of communication.
It costs more to extract cooking steam and odours into the atmosphere than just into the roof cavity so quite often kitchen companies and builders will take the ducting into the ceiling and leave that as a completed job .Often the home owner was never given the option as it may add another expense to their new kitchen.
Sometimes the retail outlet may not ask enough questions. for example the height of the ceiling as they may need to order a flue extension in the case of a canopy hood which can be costly and the owner only finds out when the hood is being installed only to find out the flue cover doesn't reach the ceiling.
So to duct out to the atmosphere or to recirculate via carbon filters?
Sometimes there is no option but to recirculate as there may be another floor above or the ducting may not be able to be concealed in a bulkhead. Then purchase a quality range hood with easy to clean filters and clean frequently.
When ducting ,the performance of the range hood relies on factors like the shortest , straightest run and the largest size ducting possible.
As for ducting into the roof cavity alone, this can be a MAJOR FIRE HAZARD due to grease and oil build-up and in the event of a kitchen fire your insurance company may find due reason to not payout on your claim.
The grease and oil creates a very tasty attraction for vermin like rats mice and cockroaches.
In closing, do your research ,check your specifications, make sure you are on the same page as your tradies.