Roof Removal Renovation Cost

I have a home built in 1970 as such it has an old style roof structure (not truss), we are looking to extend a section of the house forward and add on a veranda at the rear. From this we want to put the whole building under 1 full roof structure.
To do this does the whole old roof structure have to be demolished (im assuming this affects ceiling inside) to have a new roof installed or can the orginal roof structure be added to to exntend the roof area? We are going from concrete tile to colorbond.
There are some walls being shifted inside also.

Hey dmm12 welcome to the forum
You mean a coupled pitched roof...
It's much easier for a carpenter to add to than trusses.
The existing frame remains under the new roof whereby the ceiling doesn't get touched/damaged
Here's a roof plan & overlay it might also helps others
Cheers
Chris

Hi StructuralBIMGuy
That would be great if I could, attached is a photo ofthe house and the roof line i want to go to. Existing at rear is an extension on posts and i want to continue that across with a varandah thats approx. 4.5m and out from is an existing awning over a patio and i want to mirro that across as an extension with garages underneath.
Plus would the load on the existing be an issue?