Some building parts 'take priority' over others?

Hi.... this is driving me made

Some building parts seem to clip/clash with other parts, but it appears random in how they do this. For example, I try and build a simple house with walls and layers of floors. The walls tiles all merge nicely, and then I put a floor down to make the first storey. Then I look at the building from the outside. Now the point where the wall meets the floor (or ceiling, as it would be now) for the most of it shows the wall as the outside most layer. However, occasionally if will show the floor as he outside layer.

I cannot figure out why some 'floors' or edges of walls are hidden within the building (as it should be) and some seem to clip outside the building. I'm hoping I'm explaining this property - see the below image and pay attention to the nearest corner of the floor and the side wall it adjoins to....

Any ideas?!
This is called "Z-fighting". See
The problem here is that the game simply does not know which surface to show, because they occupy the exact same pixels.
As a result, what gets drawn on the screen is a random mixture of both textures.

Many pieces have been designed in a way to minimize this occuring, either by being "1 pixel off" or by having a surface that is perfectly homogeneous (e.g. metal walls).
Also many wall pieces have the ability to "edge together" when placed at angles, but this has be specifically designed for the individual piece, meaning it does not work in a generic way.

If you see something like this happening, think how you could change the building, so that the roof does not occupy the same space as the walls, either by moving the walls outwards, or moving the roof up.
Or cover it up, by putting decoration, for example one of the many wall/roof trims, over the area in question.
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I wish they'd change flat room pieces to be one pixel short. They're the biggest culprit of this for me. Drives me insane sometimes.
I read a trick on Reddit to get rid of the floor tile sticking out: Rotate the wall piece 180 degrees (so press Z twice) and place it in the exact same spot. Apparently the walls are not exactly aligned with the edge of the tile, so you can decide whether you want to show the border of the floor tile sticking out or not. :)

Not sure if this works for all wall pieces, also not sure if this was intentional at all. Judging from the missing pieces, inconsistent texture usage and unreliable preview pictures, it might just as well be a bug or sloppy work from the artists due to the crunch time rush, again.
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Thanks for the replies, wasn't aware of the Z-fighting thing but yeah that's exactly it. I did try rotating but it didn't seem to do anything. I was going nuts, didn't know if it was something wrong. If it's an engine issue then I can deal with that and cover over it somehow, it was annoying thinking it was some button I was meant to be pressing....