Look for everything that is not mentioned that you are expecting to be included and then check it is included, and if you are execting a certain spec make sure that is specified and what they (vs you) will be providing... a, ie windows, doors, sky lights, tiles, tiling, number of plug sockets, fitting of kitchen, demoltion, skips, rubbish removal, lighting spec, roof spec, cost for work that is not specifically in the extension but involves other parts of the house, ie radiators, boiler etc.
freddie thanks @freddie - this is really helpful. Hoping I'll see some quotes this week or next week and can dig into these. Some of the builders that have been round seem very relaxed, another firm want to send a quantity surveyor out which surprised me - all new territory for me so lots to learn.
Look for everything that is not mentioned that you are expecting to be included and then check it is included, and if you are execting a certain spec make sure that is specified and what they (vs you) will be providing... a, ie windows, doors, sky lights, tiles, tiling, number of plug sockets, fitting of kitchen, demoltion, skips, rubbish removal, lighting spec, roof spec, cost for work that is not specifically in the extension but involves other parts of the house, ie radiators, boiler etc.