We went through a major extension last year extending 2 existing bedrooms and adding 2 more. We had to sleep in a caravn for 6 months after being told it would be 6 weeks! 
Our biggest problems was we wanted a solid wood floor laying throughout the new extension and we had to wait for the concrete to dry out completely and this took weeks! I think they said an 1" of concrete drys out a month and it was few "s thick.
At least all the work was done by builders - I would have hated to have had to wait for Dh to have fitted it around his job - we've done a couple of projects on the bungalow that way - 1st a Kitchen extension and utility room added and then a large conservatory added. It does take longer!
It's looking good though Paul so it will all be worth it in the end.

Our biggest problems was we wanted a solid wood floor laying throughout the new extension and we had to wait for the concrete to dry out completely and this took weeks! I think they said an 1" of concrete drys out a month and it was few "s thick.
At least all the work was done by builders - I would have hated to have had to wait for Dh to have fitted it around his job - we've done a couple of projects on the bungalow that way - 1st a Kitchen extension and utility room added and then a large conservatory added. It does take longer!
It's looking good though Paul so it will all be worth it in the end.