Thanks @soakedat3 @avocuddl and @PazRaz10 - I'm glad personality is a sensible factor to use, as I have a suspicion the one I like best won't be the cheapest!
Re ceilings, we will have three different heights in one room - and one section is now rafter line glazing as I was worried about it being low and feeling dark/oppressive. We are also putting pins in the floor above for the roof of the extension so that the steel can sit (a few cm) higher - I may be paranoid about ceiling height!! 😂
Another question: do builders generally work over Christmas/New Year or not? Or does it vary? Feeling like it might be 2020 before we actually do any building...