It is obviously difficult to guess without knowing the extent of the works required i.e. does the deck need replacing? height of building for scaffold, what thickness of insulation (for warm roof installation). Id guess at about £35k plus scaffold costs for a proper job complying with building regs.
ballpark without looking at it would be £14000. Re covered in Firestone Rubbercover.
Our details are on the internet at Max Roofings website. I don't know where you are but we are based in the west yorkshire area and cover Leeds, Bradford, Wakefield, Huddersfield, Halifax, Burnley, Blackburn and all surrounding areas.
If you think we can help then please feel free to look us up and give me a call.
We can travel further at your expense if we need to book a room.