I suppose anyone doing a building is modeling in metric system.
Now, 1 unit in blender would be then 1 meter (this seems be now the standard).
A number like: 0.001 would be 1 milimeter and we are with 3 digits for floating point.
with six digits we would be talking about dividing 1 milimeter in 1000 parts. I can’t believe someone is doing that in architecture.
By the way try yourself to create a cube of 1mm. Now duplicate and build another of 0.1mm and you need go to orthogonal view to view it because cam is not showing it (you would need to change the planes clipping etc). But even in orthogonal there is a limite you can zoom. That means that Blender only let you model in tenths of milimeter? No, you can, if you really need to model so little, change the scale (just below of metric system button). If you have a blender cube of 1meter, changing the scale to 0.1 would convert the cube to 10meters. Then you can go and model in nanometers if you want with the scale.
Really, if any architect is using tenths of milimeters modeling a building he needs take some holidays.
Perhaps for mechanical pieces design, it be needed four digits or five in some cases of very little pieces. But I just want an example where you need seven digits. That is 10 thousand part of 1 milimeter in scale 1 blender unit = 1 meter!
In the case you need four digits from a meter set the scale to 0.01 for example