I can see from the posted picture that that particular roof section has FOUR distinct sides- each of which is angled at a slight upward slope to the higher platform in the center. ( if the building was oriented upright. each of those four sides is modeled with a “fall” to the perimeter of that roof.)
Because of this slope, the face that was affected that falls to the criple is at a different angle to the raster of the printer than are the other faces. Each of those roof planes is is at a slightly different angle.
As I mentioned before, you can get a pronounced moire effect anytime the slope is so low that it can form an interference pattern between the Build Planes and the laser stepover.
These are really mathematical artifacts delimited by the z layer unit and the stepover of the laser in trying to calculate a path the laser can draw that will intersect an angled plane.
The software can not calculate to limitless decimal places… it has to round off to the stepover of the laser controller. So as an exaggerated example… let’s say the laser controller uses integer units. each path the laser can draw will be 1 unit greater or lesser than the previous profile.
When the plane is very shallow, the polygonal data might cross the Z height at X coordinates of 2, then 3.2, then 4.4, then 5.6, then 6.8 then 7.3
and the controller- unable to do fractional widths, will round those coordinates off to, 2, 3, 4. 6, 7, 7.
As you can see this creates a bigger jump in Z height between 4 and 6- and a shallower jump in height between 6.8 and 7.3- if the plane is flat- then this series of aliasing errors will repeat at a mathematically determined frequency as an artifact of the fact that the build height and the laser stepover are FIXED amounts, whereas the data is NOT.
the lines that appeared are PARALLEL to the build plate, relative to the orientation of the model.
If you printed the same model- with a different layer thickness- you might see these lines disappear, or get worse- depending on how the math works out.
But its WHY more angled flat planes print better, because the stepover of the laser is much finer resolution than the build height.
But you will ALWAYS see artifacts of this kind emerge when printing models with lots of flat planar surfaces.
If it is an issue you NEED to solve, then one solution is to REMOVE the roofs as separate parts that you can orient independant of the rest of the building.
The printer prints accurately enough that you should be able to fit printed parts back together without significant seams.