You choose what you want to charge, work out the cost of your equipment and fuel, van repayments etc,divide by 12 to get your monthly expenses then by 4 to get weekly, then by 5 for your daily and that gibes you an idea of what you need to make each day to break even. I have a min charge for rooms up to 20m2, then charge per sq m for anything above that. If you get more than one room to do, you coud discount it as you have already made your minimum charge. The amount depends on the area you are working in, average cost of property etc .