Building a mansard roof

[HBBBCA]

I'm fairly new to Chief Architect and having to change a roof an extension from flat to a mansard at the rear only.  I'm having a hard time converting it within the current plan.  Does anyone have a quick and easy way to do this as I'm not able to find it in any of the videos or help topics? I'm already deep into the plan and don't want to have to create the whole floor again especially since it's in a terrace and affects the neighbouring houses too. I also had to fake out the party walls as couldn't find a way to do that either.

I've attached an elevation of the current roof and an example of what planning department is asking for.

Thanks in advance for any tips