Okay, so picking between mounting solar panels on a flat or slanted roof really depends on the building, how big the install is, and what you want to get out of it. Both are used a lot, but they're built differently, installed in different ways, and act differently over time.

Slanted roofs are usually what you see on homes. The roof's angle is already good for catching sunlight (sun-facing side), so the panels can be put on pretty close to the roof using simple stuff like rails and hooks. This way is cheaper and faster to put up because you don't need as many parts. Rainwater also runs off easily, and air flows better, which keeps the panels cooler and cleaner. since the panels are closer to the roof, they don't stick out as much, which is good for looks.

Flat roofs are more for businesses and factories. Because there's no angle, the mounting stuff has to tilt the panels towards the sun. These systems are either held down with weights or bolted on, so you can pick what works best for the roof. Flat roofs let you set up the panels to get the most sunlight, which means more power, especially on big roofs. SIC Solar make special mounting stuff that's shaped to handle the wind and stay put.

Putting them in is also different. Slanted roofs need to be attached just right to the roof's frame and kept from leaking. Flat roofs usually go in faster, mostly if they’re held down with weights since you don't have to drill at all. But, with flat roofs, you need to make sure the roof can handle the weight of the panels and the stuff holding them down.

Getting to the panels to fix them is another thing. Flat roofs usually have paths and space to walk around, so it's easier to check and clean them. Slanted roofs can be trickier, mostly if they're steep, which means fixing them can take longer.

The wind can also be a problem. Slanted roofs are shaped to deal with the wind, but flat roofs need special mounting stuff and weights or anchors to keep from blowing away. Good mounting parts are made to handle the wind in both cases.

How much power you get really depends on how well the system is designed, not just the roof. A flat roof system that’s set up well can beat a slanted roof system that’s facing the wrong way, and the other way around. The roof's condition, how much space you have, the weather where you are, and what you plan to do long-term all matter when picking the right way to mount the panels.