My thread might help a bit 
The second lesson should be ready within the next few days, which will cover bytes themselves. Right now it's pretty basic stuff but in the coming weeks the stuff it goes over will help with understanding file formats and consequently creating your own, too.
In any case, having some experience with hacking/understanding existing formats (even popular ones like PNG) is definitely a gigantic help, and I would highly recommend looking into that stuff if you haven't already.
I have to ask though, why? Most of the weird formats games use are due to requirements rather than choice, because they're using a custom engine. If you're working with Unity, there's no reason to create your own format, unless you want to prevent people from ripping your resources. And in that case, just encrypting them with a standard algorithm will be more effective.
I understand creating custom formats out of interest or necessity, and that case I totally say go for it. But if you're making a game with Unity, I just don't see why you can't use good, well-supported, functional formats.
The second lesson should be ready within the next few days, which will cover bytes themselves. Right now it's pretty basic stuff but in the coming weeks the stuff it goes over will help with understanding file formats and consequently creating your own, too.In any case, having some experience with hacking/understanding existing formats (even popular ones like PNG) is definitely a gigantic help, and I would highly recommend looking into that stuff if you haven't already.
I have to ask though, why? Most of the weird formats games use are due to requirements rather than choice, because they're using a custom engine. If you're working with Unity, there's no reason to create your own format, unless you want to prevent people from ripping your resources. And in that case, just encrypting them with a standard algorithm will be more effective.
I understand creating custom formats out of interest or necessity, and that case I totally say go for it. But if you're making a game with Unity, I just don't see why you can't use good, well-supported, functional formats.