I used bar and chain oil - always have a few gallons handy. Water is fine for shallow drilling and mortar or fresh 'crete, but even drilling 3/4" dia holes to 7" depth in fresh 'crete, I was having problems keeping things cool, and I had more than 100 holes to drill.
You have fewer holes, may...
Assuming you can't drill and set masonry bolts in those stones, and simply chain the thing down, I'm not hearing other options.
and I have clay-y sands and sandy-clays - I LOVE my Rotary Hammer, but there are plenty of rocks I won't put it to. The native limestone, sure - like butter. But you...
I'm pretty happy with my DeWalt, too - but mostly have Bosch corded. Except for roofing, where battery powered impact drivers are nice, I MUCH prefer power tools connected to actual power. Have had terrible experience, not just with battery life, but with battery changes - its planned obsolescence.
when I built, instead of using the traditional 1x4 purlins, I used the 5/4" x 6" (actually 5.5" of course) Pressure treated wooden "decking" boards. Obviously sturdier from the greater thickness, treated against moisture, and being a bit wider, it was easier to "not miss" working alone screwing...
Metal roofing is cheaper than decking, papering, and shingling - more durable, too, and more likely to be installed correctly. We have differing wind concerns. I'm in FL - gusts of 70 mph isn't a concern - we see that with some frequency as part of regular summer thunderstorms. 100 mph+ is -...
I think its overkill, and wind uplift is only a concern if your roofing material is strong enough to take those loads. If you use metal roofing (cheap, easy, fast, durable), it will fail either where the screws penetrate the purlins, or where the purlins are affixed to the rafters before it...