I would never ever charge by the hour, i find that clients end up watching what your doing and counting the hours. In my experince i have found its best to either charge 1- By the number of people whom im cooking for + the cost of the ingredients 2- By the day 3- By the week I'm guessing like me most of your clients would be very weathly so i was to charge 200 pounds per day this seems like a good deal to them Also if i were you i would call up a few local chef agencies and ask them to tell you how much a head chef is per hour this would help you to work out your costs, in london its around 20 per hour i found out