I suspect you are biting off a much bigger chunk of food that you think: writing an OS from scratch is not a trivial task! Heck, when the PC was first invented, IBM didn't write their own OS for it, but bought it in from a tiny company running out of a garage called "Microsoft" - and at the time, IBM was the biggest computer company in the world...
It's as big job, particularly if you want to produce a Graphics based OS rather than the much, much simpler text based OS that MS provided.
But...
create operating system - Google Search[
^] will give you some very good resources to start from - with a serious amount of reading for you do first. There really isn't a good sport cut here - you have a serious amount to learn before you get anything useable up and running.
Good luck! I hope you persist with this, and succeed.