I made the beginnings of an operating system with a computer I designed and cobbled together years ago (I think that would be about 1985 or so). It is decent fun and you learn a lot doing it. Good success on your project!
The answers people have been giving you about a platform you could use to develop your operating system have been of the hardware variety. You would have to spend a bit of $$. Assuming you have access to a computer you might consider using a virtual computer like QEMU, or Oracle's Vbox and develop an os for that. If you have a mac, I really like Q as the interface makes the virtual computer even look like one. I think other posts here have probably mentioned osdev.org. That is a great place to bounce ideas off other DIYers, and get some help getting started. Good success to you.
CHEERS
