Victorian Bay Roof Parts

[rideforever]

Been having the beginnings of trouble (dampness inside) under this roof and I have been wondering how hard it is to repair. It seems to me that if I get a scaff and take the tiles off and timber and just replace like for like it can be fixed without too much trouble.
Only thing is between the faces there is a sort cast masonry "cap" that covers the joins between the faces. This is poor condition crackes and repaired. How can this cap be remade? Can you buy one or do you make it in a form ? Or do it in situ?
Thanks
(please ignore the red arrow in this photo)

 

[datarebal]

Strip and re tile and use baby ridge

 

[rideforever]

Strip and re tile and use baby ridge

Thanks ... do you know if originally a form was made to cast those ridges in?

 

[datarebal]

Probably strong mix coloured mortar . Formed in situ.
The picture isn't perfect