я сам себе человек - we wouldn't say that. If I understand what you are trying to say, we seem to have several phrases that can be chosen in different situations. For example:


я сам себе хозяин - meanings: I am my own master, I am my own boss, I myself control my work and actions.
я сам себе начальник - in work situations can mean 'I am my own boss'.

There might be other similar phrases but I can't take any more right off my head, the idea is 'I control my actions myself'.