You need a slow careful survey, or ask the construction manager about the studio as we have generally worked in all of them. Another time not to allow yourself to be rushed is during a survey. If its a build on location, allow yourself leisure to go around the room several times and draw it in your notebook more than once. A photograph of each angle is always handy if you are working out a missing dimension at your desk later, you can always look at a dimension on the image that you have and work out an approximate dimension for the one you are missing. There is even software available, that does this for you.