Aren't imperial units considerably easier to calculate on the fly in construction and when squaring? They seem to come more natural for me.
Actually civil engineering as a whole is probably a relatively mixed bunch – vehicles drawings (when you need to design the infrastructure to fit specific vehicles for example) and other small-scale details might be dimensioned in mm, the standard curbstone naming system in Germany is based on centimetres, while infrastructure design itself (definitely including the CAD drawings) usually works in metres.
12 divides cleanly by 2, 3, 4, 6
10 divides cleanly only by 2 and 5
Obviously downvoters who've never used a speed square nor tape measure before.
When things are not nice round units though both systems are equally hard. This is common in the modern world where we do a lot of things impossible 200 years ago.
in reality you almost never calculate on the job. You measure what is on the print and anything not on the print is figured out 'when you get there' by measuring the space left when you get there - which also corrects for previous measurement errors
I tried asking on a forum once on how this impacted default room sizes. I see standard ceiling size in the US is moving to 9 feet. I am assuming places on metric would not standardize on that number, but curious if they would just stick to the nearest half, or go to the nearest whole meter. (I "tried" asking, as people seemed to think that you would just design the room to be 2.74 meters and call it a day. That strikes me as very unlikely, as design tools really love "snap to grid.")
Now if we used base 12 numbers instead of base 10, and we had a system of units based on that, I bet we’d have the best of both worlds. No idea if Napoleon could have imposed base 12 arithmetic on most of Europe the way he did metric, though.