First, it's not as easy as it sounds. You'll need a lathe as well as a mill if you want to scratch build, and a solid knowledge of metallurgy and heat treating procedures (and equipment), as it's not as simple as cut it and use it.
On a cylindrical bolt action, a mill will be used to do the loading/ejection port, trigger and sear accomodation, locking areas, and it's possible with the proper tooling to work some kind of raceways. (I'm honestly not sure how the big makers do action length raceways, broaching perhaps.) That leaves a lot left to do, some on lathe, some perhaps by other methods. In the end, you're better off to take the gunsmithing course at SAIT and just play with rebarrelling commercial actions, but this is just my opinion, though it will be cheaper.