Well, rooftop, while definitely better than using farmland, is less efficient than commercial ground-mount and your exposure time is also typically less because of the less than ideal angles.
Let's do a nuke to solar comparison, lol.
Darlington is oft cited as being able to power 2 million homes, with a nameplate capacity of 3,512MW.
If we wanted to match nameplate, we'd need, obviously, 3,512MW of solar; 3,512,000kW. So, if every house had an 8kW system, that's 439,000 homes. However, the nuke produces ~90% CF, so, over the course of the year, it produces 27.7TWh; 27.7 billion kWh. Now, here in Ontario, rooftop solar would be lucky to have an annual CF of 10%, but we'll use that for the sake of this example.
So, 90% CF for the nuke gives us 3,160.8MW
10% CF for our solar panels yields 351.2MW
We are going to need some more panels.
Working that number backwards we end up with 31,608MW of solar needed; 4 million homes.
So, we'd need 4 million homes worth of solar panels, to provide enough power to run 2 million homes? That's how the math works, lol.