I would have flat roofs to if I was making the buildings. 
Fortunately for us, you aren't. If there are approximately one hundred buildings in that city, a division solely for the sake of example would have sixty of them being the filler while thirty-five are the factories with smoke stacks, and the other five being flak towers. The sixty filler in game have, at minimum 5 polygons, one for the roof and four for the sides (I do not know about the bottoms of the buildings, as I know very little about how the magic works). So, sixty times five gives us 300 polygons. If the buildings have floors added in, we would have 360 polygons. Your buildings with angled roofs have at least 6 polygons, again without floors, giving us 360 polygons. If there were floors, that would be 420. The destroyable factories would have around 17 polygons, without floors, giving us 595 polygons. With floors, there would be 630 polygons. The flak towers would each have around 26 polygons, with out bottoms, giving us 130 polygons. With floors, there would be 135 polygons.
Now, with my (VERY) conservative guess as to how many buildings there are, we would have:
Without floors: With floors: With roofs, no floors: With roofs and floors:
Filler 300 360 360 420
Factories 595 630 595 630
Flak Towers 130 135 130 135
Total: 1025 1125 1085 1185
Having the angled roofs gives us a total of 1185 polygons, which is 160 more polygons than flat roofs with no floors, or 60 polygons more than flat roofs with floors. But wait, we have not yet added to this however many polygons it takes to build the various environmental objects, your plane, and the planes around you. When we take these other factors into account, I would much prefer to have a game that can build my view more quickly, at a more consistent rate, and with higher frames per second on a 256 MB graphics card over prett(y/ier) buildings.
