I learned the hard way how to go out and measure up Location Elevators. They nearly always require a matching set-build, because they are for the most part unshootable without wilding walls. They are too small. They are often reflective.
I used to toil away, sketch every detail in my quad pad, measure every increment, note every detail.
Not every location elevator had a key, so I was often making new friends and answering a plethora of questions as to wtf I was doing in the elevator?
Needless to say, I spent a long time in there, going up and down.
Then, around the time that I got my first digital camera, during a hectic prep, I was just plain out of time. I took overalls, then I just shot the hell out of it with my camera, placing my tape measure in the shots as a scale.
To this day I still do it this way.
I just email all the photos to the Construction Dept with a basic plan & Elevations.
Elevators are 90% moulding and panels. Its just too hard to jot it all down and get it right.