Desktop/laptop users can click on the images to enlarge them.
(Keep in mind that this is only usefully accurate for low-slope or "flat" roofs. For help with sloped roofs, see here. And even "flat roofs" usually have a little bit of a slope, so you might want to use a roof pitch multiplier once you have your area figured out.)
1. The first thing you need to do is download and install Google Earth Pro. Google Earth Pro was the paid version of Google Earth (it used to cost $400 a year), but it’s free now. It includes tools not available on basic Google Earth, the most relevant being a measuring tool that allows you to measure the area of a polygon. You can download it at: https://www.google.com/earth/versions/
2. Once you’ve installed Google Earth Pro, open it. You’ll see an image of the Earth along with various menus and tools around the edge of the screen:
3. Make sure the box for “3D Buildings” is NOT checked. 3D Buildings mode can interfere with your measurements. The 3D Buildings option is located under the “Layers” menu on the bottom of the right side of your screen:
4. At the top left of the screen, you’ll see a search field. Enter the address of the building you want to measure in the search field and click on “Search”:
This will put a pin on the location and the image field will zoom to the location and center itself on the pin so that you can see your roof: