OSdev wiki is really the mecca when starting the build your own kernel. I've used it almost exclusively while building my own [1], thanks to this tutorial [2] osdev I have just finished pre-emptive multitasking!

However the more a kernel mature the less these tutorials are useful, for more advanced topics there will only be a few open source implementions to take inspiration from, usuaully linux and the BSDs.

[1] https://github.com/jzck/kernel-zig [2] https://wiki.osdev.org/Brendan%27s_Multi-tasking_Tutorial