If you are gathering a selection of quotes from different firms, it's important that you don't just opt for the cheapest price you're offered. While we're all looking to save money, this shouldn't be at the expense of a quality job that will stand the test of time. Ask what guarantees and certifications the builder offers on the work they'll be doing. This is especially important if you plan to sell your home in the near future. It may delay or even lose you a sale if you can't prove the work has been carried out to a high enough standard.