Our budgie trusts us (our family and even strangers who visits) by flying around us, clinging to our hands, shoulders and heads. He is even more talkative and playful when freed from cage. The only thing that concerns us is why is he still afraid of our fingers, yes, he sometimes steps on our fingers but always avoids it when we attempt to scratch like he's disgusted or something, he even bites hard at times. It's like he thinks that our fingers is a separate being and not a friend. We are not too aggressive on pushing our luck with our fingers as well. Is there a way to extend our relationship with him to our fingers as well?
It is quite possible he doesn't want to be scratched, not all birds enjoy being pet.
However, the best bet you have is move very slowly and to let him come to you. Will he eat out of your hand? If not, working on that is a good first step.
Then, with a supply of very tasty snacks, you can get him used to your other hand moving slowly around him (not toward him yet). Work on this a little every day until he is no longer nervous or distracted by your hand moving slowly in the general region of his body.
Next, start getting closer to him gradually. Back off if he seems nervous or distracted, and keep offering him food he likes with the other hand. Eventually, you'll be so close you're touching him. Make sure he's very familiar with the idea of feathers on skin before you start doing anything with your hand. It will take quite a long time, probably weeks, but he will either get used to it or clearly let you know what his limit is.