How do I install the valleys

I assume this is corrugated metal roofing in long sheets? Are you nailing it over an existing roof deck or just directly to rafters? Basically you put a flat valley sheet on first or a series of two sheets the first one narrow covered by a wider top sheet to channel the water into the valley, then bring the roofing down to it from both sides overlapping it. Keep any nails you are using on the corrugated panels don't nail into the valleys or they might leak.

See this link:

http://www.jenisysep.com/downloads/details-postframe.pdf