How can I build an operating system completely from scratch?

I am interested in building an operating system, but not sure where to start, whenever I search in google it frequently throws up pages about re-creating linux and stuff, but I LITERALLY want to create it from scratch, like writing my own files etc.

Is there a book on this or a tutorial on the internet?

Well you need to start with some design specs long before you start thinking about writing any code. That is for example outline what you want this OS to do and support on what hardware.
You will also need to be fluent in operating systems architecture as there is a whole world of issues to content with.
If you want some pointers tell us what you know about OS architecture, hardware design and programming.

I would say learn assembly. You will need to know it in order to do a lot of the low level interfacing with the hardware.