Yeah, I'd be interested in doing something like this too, I guess im more curious as to whether I can do it or not. Obviously as others said, theres plenty of customisable options out there, but also be nice to make one. And if you did a good job then might make some money from it. But from my (small) coding knowledge, flutter would be a good choice as its cross platform, so learn a bit of dart, then go flutter as thats what its based on.
If you don't know how to code at all, definitely go to github, plenty of apps there you could fork and customise or even just learn from reading the code. Github is a great place. I would advise against using frameworks if you dont know how to code cos you're kinda doing it back to front then and future versions/bugs that need fixing will be much harder that way.