Tricky one to be honest if you're looking to do this legally. Any sort of education or teaching business will require permission from the Supreme Education Council. First you would need to set up the company, which is a costly business. If you decided to do this without the correct permissions, you are taking a risk, though it seems many do it and get away with it. Qatar has no system in place to support small businesses, though some manage under the sponsorship of existing companies. That said, they're never involved in 'education'.
Your best option would be aligning yourself with one of the schools here, if that is a possibility.
There is no such thing as Freelance in Qatar, as you have probably be in the UK.
Sorry for the negative answer, but it's better you know the facts!!