Instead of thinking about it as 'making your own religion', think of it as if you're making your own IDEOLOGY.
We ALL have an ideology. It includes our beliefs, our logic, and our morality. So look at the one you have now, and look at the life you live, and about what you'd like to change.
You'll eventually figure it out, but here's some tips. Figure out your values, and ask questions about them. Logic is King, but it depends on a premise. Use the "most true truth" you have and put that as the premise of your belief system. The rest is just a matter of understanding logic and applying it to your life. But a purely rational thought pattern doesn't work, since humans AREN'T purely rational. So you need something basic to serve as a moral compass.
That concept is NAP.
You'll eventually have to deal with harder questions, so make sure you keep challenging your preconceptions. Vet everything about your beliefs even more carefully than you vet your news. And think about ALL possibilities. If something is possible, it's irrational to dismiss it, no matter how 'impossible' it appears to be.
You'll eventually be faced with the question of god. Practically speaking, most people misunderstand the question. "Does god exist" depends heavily on your interpretation of "god" and "exist", so in order to answer it rationally, you need to define those things first.
Eventually you'll realize that God is just a word that you can use like a tool. And you'll suddenly find yourself becoming increasingly theistic to the point where you literally feel like you're going insane because it makes so much sense and yet NO ONE ELSE seems to agree with you.
Except random anons on pol, ofc. Outside validation helps ground you.
If you just focus on self-reflection, logic, and compassion (nap), you will be able to slowly work through all the bullshit lies you've been fed. They say the truth hurts, but the truth is, it doesn't hurt at all. It's the LIES that hurt us.