Storing your roofing materials in the rain is normally a bad idea.  It is difficult to dry out the materials prior to installation and violates most roofing manufacturer’s installation recommendations/specifications.  Not a great idea to install wet roofing materials which they were about to do on this job site.  It’s pretty easy to put a tarp or plastic on materials stored on a pallet so storing your roofing materials in the mud and rain may also indicate the general care in your construction.