In recent solar visits to customer residents to evaluate their prospective solar installation, I have chosen to go old school first. That means getting on the nice warm roof and getting a full visual of roof slopes and pipe risers through the roof and those vent circulation fans. Taking actual measurements, yes with a measuring tape. And taking photos so I may recall areas on roof top.
You will then find out for yourself, that not every square meter (solar measured in 1000w/sq. meter) on a roof top will generate the data found on a panels specification sheet. Thats due to the angle(solar zenith), direction(solar azimuth) of the roof top, oh and your location on earth.
I then take this old school information and consider it when I start to use solar rooftop layout software. Now its nice , to just get into the software and go Gooogle Map and place panels all over the rooftop. But we can’t get all carried away and inform customers of incorrect data and show them a greater return than what reality will result. What we can do though, is provide the most efficient solar panels, optimizers, and inverters, with the most return for the buck.