Is spray foam a good option for wet areas in roof space?

Do not have the spray it causes all kinds of problems don't waste your money on that you may be able to fix the leak whatever you do don't have that spray

No it is not a good option , once the underside of the roof is sprayed the tiles cannot be used again . The best option is to have the roof stripped , new felt , lathes & re-use tiles. Presumably if you are in a block of flats your neighbours should be jointly responsible for the cost. If you are a leaseholder you will need to speak to the freeholder or their managing agents to discuss the roof , get permission & see if there is a reserve fund for this type of work or not. Also confirm with your solicitor the joint responsibility & how you should go forwards