Marking out tiles for a lead valley

[jackg]

I can't find anything specific on how to set out tiles prior to cutting them for the valley.
I have seen a comment that tiles are set two tiles away from the valley and a string line used to mark them for cutting.
Do you fit the only tiles either side of the valley and mark them with a string line and then cut them and then fit the other tiles above them or do you fit all the tiles either side of the valley and then mark those to be cut?
The tiles are clay double roman and the valley is lead lined with a tiling fillet.

 

[datarebal]

To be honest you can cut them anyway you want .
The chalk line works well with careful measuring.

 

[jackg]

Thanks, I thought it was some mysterious technique known only to roofers.

 

[^woody^]

Thanks, I thought it was some mysterious technique known only to roofers.

That's why no-one will tell you.