I'd like to talk a little about a vertical axis wind turbine positioned on its side. Yeah, I know, it becomes a HAWT when you do that. The main problem is that, in that position, it doesn't spin from all wind. But there are some advantages. Firstly, it is low profile and neighbors are less likely to complain. Secondly, it is technically easier to mount this way. Standing straight up means the mount point has to be way stronger due to massive torque effects. And thirdly, you can link several wind turbines in a row to share shaft power to one powerful generator.
There is also an advantage to putting a VAWT on the rooftop. When the wind comes, it is compressed upward and effectively gives the savonious more surface area of wind collection. If the wind is traveling perpindicular to the axis then you will get your maximum power potential. In the below example, there is a VAWT 8 feet long and 4 feet wide and it s laying down on its side at the rooftop. In this example the roof rises 8 feet. That means that whatever power the wind turbine would generate in a given wind is multiplied by 3. Of course, a different roof and sized wind turbine would generate different results. So, if it ran at 15 % efficiency normally, then on the rooftop it could be up to 45% efficient. Also note that wind at the peak of the house is stronger than wind at the ground level.
In the below picture you will see wind angles at 45 degrees from perpindicular to the axis. At 45 degrees, the wind turbine should appear to have half the surface area. So, half of 45% would be 22.5% efficiency, still good. At 60 degrees off perpendicular, the silhouette would become one third of full and, in spite of the roof, would make the overall efficiency become 15%. In other words, you can get normal power even at extreme angles. And at perpindicular angles, get 3 times the normal power output.
Some roofs have sections that are perpindicular to each other. Another VAWT could be mounted there as well. That way you generate power no matter what direction the wind comes from. And even if you only have one, whenever the wind direction changes back to a better angle, the power increase more than makes up for the times when no power was generated. Just make sure that your predominant wind is the right direction, otherwise this just wouldn't work for you.