Broken hip extension

Hi All,

I am doing an extension with a reasonably complex roof. There are some parts that I am looking for best practise on.



The thin blue lines on the right are the existing building(fat blue lines on left are steel). For the valley of the extended roof I was going to use a scotch valley style to avoid having to redo the existing roof there. for the outside (marked in yellow) can I also use the equivalent of a scotch valley or do I have to remove the existing roof struture and replace correctly as shown above (with a flying hip at the top to cater for the lower ridge line on the extension).