I also never used one, however I heard a lot about CleanBid and I know that they are constantly updating it and adding new features. I thing they used to have a free trial before, not sure if they have now.
Measuring is important for carpet cleaning, stripping/waxing jobs. However for regular cleaning I never measure, I just make notes on how many offices are in the buildings, how many cubicles, conference rooms, number of entrances, number of restrooms (size, type of floor, number of sinks, urinals, type of paper/soap dispensers). Also I write down how many restrooms are in the building, number of tables, chairs, microwave ovens if they have to be cleaned. Number of floors, are there elevators or you have to use stairs. Is janitor closet on each floor? It's important because I have one old account where I have to carry bucket with water in hands on the second floor and back.
Make yourself a list of questions you feel are important and while you are there fill in as much information as possible, because if you don't do it you may forget it later, especially if you have a few walk throughs in one day.