Converting a garage price

[sattyb]

Hi,
I'm looking to convert my garage into a habitable room. The garage is approx 5.5m x 2.5m so sort of standard size.
I also want to raise and replace the roof of the garage so as to get decent height in the new room.
I've been quoted £9k and £10k which includes raising and replacing the roof and all electrical, insulation, plastering, new window and radiator and sockets.
Does this seem reasonable?
I'm in SE of England and West of London if that helps.

Thanks in advance.