Don't always trust Google Earth.
When I had my metal roof put on, the company rep came by and told me the estimate was wrong and it was 10 squares short. I forgot the equivalent of a square. Anyway, he asked me if I would cover the shortage. Seeing as the roof was finished and only the permit was still open, I told him too bad, see your salesman, it's his mistake. He started crying that it was equal to about $2000. Tough patooties dude, he works for you, not me, dock it from his pay.
It seems instead of getting on the roof and physically measuring it, he used Google Earth. I also called him on it that if the calculations were incorrect, why was the proper amount of material to complete the roof on the ground? He didn't have a thing to say.
I think he was looking for a little pocket money myself. It may have been an insurance payout, but i still spend it like it's my hard earned money.
Yeah that's too much precision to ask of Google maps. Especially in a business deal. That guy sounds like a jackass.
But I've personally verified it's accurate to within a tenth of a mile over a distance of 20 miles though, in a straight line.
We can do this in Illinois because it's flat land and all of our farm roads run either perfectly straight north/south or east/west because of the way the land was originally surveyed. No contours in the topography to work around.
Anyway my dad put a digital speedometer/odometer on his fancy expensive "cat trike" bicycles. Tricycles..
Anyway my neighbor & I used one of those wheel measuring things with his golf cart to verify it a exactly 5280 feet from the center of one road to the center of the next one parallel in the one mile square grid. We did that so my dad could check the accuracy of the bicycle speedometer.
We also towed my dad on the bicycle up and down the road with the golf cart and my 4 wheeler, using a GPS on the tow vehicle to compare the speeds and it was accurate up to the point where the wind and exhaust noise was too loud to hear the speeds my dad was yelling, which was about 35 mph.
After making sure the bicycle speedometer/odometer was accurate with its tires at 100 psi, he kite-towed it to Grant Park and sailed it back with a homemade sail, without wandering around in Grant Park. It's exactly ten miles, straight line, and he turned around and came back. It was 20.00 on the odometer and when I measured it in Google Earth it was 19 miles + 5292 feet, twelve feet over... the approximate distance traveled during his U-turn.
But no, you don't measure for roofing materials with Google Earth unless it's big Amazon warehouse or a Walmart supercenter where the percentage of error won't matter.