I know that it depends on what you are having done but is there a list of things you need to source/research prior to the start of an extension? I would like to be super prepared for when the work starts and want to avoid the scenario of the builder saying 'we need all the door handles and light switches by tomorrow' and me dashing out and buying expensive stuff I don't like. There are bound to be things I would never think of. Having a complete list (sourced and priced) should also help with keeping tabs on the budget, no? We are having new bathrooms, bedrooms, utility and kitchen.
I have visions of creating a marvelous spreadsheet, possibly with colour coding.... 