The best way to follow up after the rolling magnet is with a metal detector. I bought HF's TSA-style detector
back when they were cheaper, and use it all the time when I'm ripping used lumber into orchard tree props. For that mess in my driveway where the roofer's truck spilled roofing nails, I went over the parts with deeper gravel using this detector. I found a few more roofing nails that the rolling magnet had missed.
I use it often to find a dropped screw, nut, etc that somehow went invisible as it rolled away on the garage floor.
I see that HF now sells a cheaper $16 handheld metal detector. I would definitely buy one if I didn't have the larger detector already.
Thanks CA, et al,
We appreciate the support & commiseration!
While the Roof Boss appeared embarASSed and showed proper chagrin at our little presentation, we'll be keeping a very close eye on his figures for the fascia and gutter jobs we added on after we saw how the roof looks.
Our house is a log construction with SYP logs stained with red cedar CWF Sealer over the 21 years we have owned and lived in it, so the Forest Green steel roof makes for a really nicely contrasting color scheme.
The metal-detector for back-up against any missed sharps is an excellent idea, which I hadn't thought of. Looks like I have a reason (excuse) to take my percent off coupons on a visit to our HF!
What we did so far, in lieu of that, was to make multiple trips in a crossing grid pattern and where there were clumps of leaves, we raked them out and went over them several times in multiple patterns as well, in each case until a trip (or usually more) went by without any more of the loud clacks that signalled more found nails.
The area where they had the dumpster parked, and therefore spent most of their time throwing the debris off the roof, is our usual parking area, so despite the long winter, the gravel is well-packed and without any loose gravel areas where the nails could get mixed into it, so we figured our approach would suffice for now.
That being said, the cost of the HF metal detector would quickly be recouped by saving us from one flat tire, or finding even one of those "disappearing metal parts/pieces" from our barn floor or driveway. Also, if you don't already have one of their black plastic headed, yellow shafted magnets on a stick:
Long Reach Magnetic Pickup Tool with Quick Release, it's worth getting one, because ours has saved us untold numbers of times by finding and picking up lost and dropped screws, washers, and other miscellaneous ferrous parts. Don't ask how I know it can find truck AND car keys dropped into 3+ feet of loose snow...
Now, if they only had pick-up magnets for non-ferrous, and plastic parts.