Satellite Images and Roofs
1. General: Google Earth Pro is now free. The download is available at the Google Earth website. Take advantage of the full range of measurement tools that you used to have to pay for.
This is great. For one thing, you can zoom in on the roof and use the polygon measuring tool to plot the perimeter of the roof and get a usefully accurate total square footage (for "flat" roofs; sloped roofs are a little more involved, see here for help figuring out the area of a sloped roof). Zoom in on the roof, then select "Tools" at the top left, then select "Ruler". It's pretty self-explanatory after that. If the angle changes too much when you zoom in, go to View at the top left, then click on Reset at the bottom of the drop-down menu, then click Tilt.
2. General: See this article for help with using the measuring tools on Google Earth: "How to Measure a Roof with Google Earth".