The question is why would you want to do this?
I can see messing around with an arduino
I can see getting a job where you make computer parts (electrical engineer or something)
I can see having a hobby of building computers in unconventional ways
I can't see making a computer that is going to so primitive its going to be borderline useless. This would be if you are starting from complete scratch tho.
Unless you are talking about getting a bunch of computer parts and wiring them up to a circuit board. I mean. I guess it would kinda be like adult lagos in a way. But you should prolly learn how to solder and stuff first. Regardless, its going to take some knowhow of circuits in general. You can fry shit pretty easily (like capacitors and resistors). Luckily there are computer part stores that sell a lot of stuff that is already kinda halfway made already.
Some stuff you would need:
Power supply (easy enough to make one)
Digital Multimeter (I would go for a good one)
A website where you can buy computer components like timers, capacitors, circuit boards, soldering equipment, resistors and the like.
A book about how the computer components work (and how voltage, resistance and current will work in your computer)
Not and exhaustive list, like, at all.