You want to build your own CPU? That’s great fun, but you might find it isn’t as hard as you think. I’ve done several CPUs over the years, and there’s no shortage of other custom CPUs out there ranging from pretty serious attempts to computers made out of discrete chips to computers made with relays. Not to trivialize the attempt, but the real problem isn’t the CPU. It is the infrastructure.
What Kind of Infrastructure?
I suppose the holy grail would be to bootstrap your custom CPU into a full-blown Linux system. That’s a big enough job that I haven’t done it. Although you might be more productive than I am, you probably need a certain amount of sleep, and so you may want to consider if you can really get it all done in a reasonable time. Many custom CPUs, for example, don’t run interactive operating systems (or any operating system, for that matter). In extreme cases, custom CPUs don’t have any infrastructure and you program them in straight machine code.
Machine code is error prone so, you really need an assembler. If you are working on a big machine, you might even want a linker. Assembly language coding gets tedious after a while, so maybe you want a C compiler (or some other language). A debugger? What about an operating system?
Each one of those things is a pretty serious project all by itself (on top of the project of making a fairly capable CPU). Unless you have a lot of free time on your hands or a big team, you are going to have to consider how to hack some shortcuts.