How do i cut and existing overhang?

[Wagurto]

I need to demolish a roof overhang and a part of a roof but split tool does not work on roof. How do I change existing part of a roof to shown in demolichion phase.
thanks

[Scott Hopkins]

Copy the roof to the exact same place.

Edit each one so that one copy of the roof becomes just the part you are keeping and the other copy of the roof becomes just the part that you are demolishing.

[beegee]

Model the existing roof in two parts to reflect the section that will be demolished.
Then use 'join geometry' and then demolish the existing overhang in the demo or new phase.