The real scope of the project is not known. As I said you must discover the true requirements. Even if you just did exactly what he said, they always change t

The real scope of the project is not known. As I said you must discover the true requirements. Even if you just did exactly what he said, they always change their mind and add more. Fixed scope is as I said a fiction and structurally false. If your goal is to try to sell him a large sum and then come out ahead by easily completing the task in a relatively short while, just realize that he has a similar but opposite goal with such a structure. And even if he isn't trying to squeeze as much work out as he can, like I said the scope always increases naturally. What you do need to do is make sure that he has a budget sufficient for his ambitions and if he doesn't make it clear that you believe that will limit the success of the project. If you want to make a lot of money by selling something for an outsized price, then maybe become a used car salesman or something. Having said all of that then if possible bill for half-days or full days. Just make sure he agrees ahead of time.