I hired a roofers to do the newly built extension, main house and the newly built porch roofs. they have done a good job up today. all the roofs completed apart from the flash lead of the porch in particular the corner where the porch pitched roof meets the house wall which are perpendicular to each other see attached pics. they said this need a led man to do because they can not guarantee it is not going to leak if they did. I live in Wiltshire, any idea suggestion how this can be done please. is there a places when it can be fabricated