Rear Extension and Extra Bedroom Extension Help!

Hi Everyone, We are new to the forum, a couple living in the East Midlands. For various reasons we would like to add an extension to our existing 3 bed detached new build (3.5 years old) house. We can comfortably extend out at the back to 3.1m and our initial thoughts are to extend all the way across the back of the property, and then either add a 4th bedroom in the loft (if budget will allow) or maybe a partial second storey extension to create the new room.

Thanks for your reply, we are going to consult a loft specialist on Monday to see what can be done with the loft, it is W trusses, however the people we did speak to did say that the roof doesnt need to come off but structural steels will be required to take the load of the roof. We did consider opening the landing window and having a room off the back of the house, but the distance between the two bedroom windows is only about 3m so we were worried that the internal dimension of the new room w