Installing roof snow/ de-icing heat cables on roof...?

The zig-zag pattern is to cover a wider area along the eaves. That is not required for a valey. Bear in mind though you need to to place the retainer clips onto shingles, that might be an issue with a metal valley. I ran mine up one edge of the shingles, across the valley, and down the other shingle edge.

It's worked well so far.