It really depends on how much you want to earn.
What does the life you really want to live cost you?
Examples could be if you want to live in a council house and drive a 10 year old Citroen, your hourly/sq m rate will likely be low.
If you choose to live in a large detached house, drive a big fancy car, go to restaurants a few times a week, go on lots of holidays around the world - your hourly rate will need to be higher to achieve this.
it's better off you starting at the END - what does the end look like? Once you figure this out, you will know what to charge per sq metre to meet that end goal.