Need help with a build

Hi! Me and my friends are trying to build a specific house, and we are having immense issues with a mansard.

Basically - due to the shape of the roof whenever we make the mansard room it's first of all impossible to place items in the majority of the room space AND you can't really see anything in it as roofs cover all the visible space. The room walls also poke through the roof, but that we can cover with greenery.

Is there any way to make it real? Please help