Unless you are prepared to climb on to the roof to put a cap on in place of the pot then its a profesionals job. Get Three estimates. And if in UK ( its a world forum) check with your local planning department if the flue needs to be lined as its only an electric fire.
Why? to stop you being conned by builder/roofer saying it needs lining. However if you think you might change later to a gas fire then it WILL require lining and the flue/pot capping replaced for a suitable chimney/liner type cowl.
bob
June 2012
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