I recently bid on cleaning a commercial building roof. I have used the ruler on Google Earth to track hikes, paddle and driving trips, but never to measure down to feet.
I tried it on this building and got a measurement of 65'x192'. Since total accuracy isn't as vital on a cleaning as a repair, I used those figures and got the job.
Yesterday, I needed some oil and there's a NAPA store in that building, so I went there and checked on the measurement at the end. I got 64' 2". Tack on the width of the gutter on both sides and that 65' figure I got from Google Earth is impressive.
Eagle view will do it for you for a small fee. it breaks it down to a gnats eyebrow.