adding insulation and new felt over existing flat roof?

Hi

Could someone advise me.
Our flat roof covered in felt is bubbling badly. We have arranged for a roofer to replace the felt on the existing deck which he said was sound. Today he looked at it again and said that there is asphalt below the felt so that the felt will not be easily removed. He now wants to cut out the bubbles, put the insulation on the felt and then cover with 3 layers of felt- is this OK. He also recommended using flasband rather tahn lead flashing.
I am a bit worried about the loading and did not want a patch up job but a proper one. The flat roof is approx 20 feet by 10 feet.