Mains Power Cable DIY

I'd like to DIY a main power supply to my system.
I'd like to do this in two or three stages
1st to build a power cable from the wall to my amp
2nd to build a mians distribution for all the gear

And 3rd: I'm waiting to renovate my condo.
At that time I'll have a primary circuit from the panel to stereo run
If anyone can offer their experience and specific details I'd much appreciate it
Currently I'm running an old "gang box" ....something I made during my construction days. Tonight I took the wall socket apart , cut it back and reconnected everything and there was a fair difference in what I heard.
I'm specifically looking at wire sizes and recommendations for shielding and what it all looks like. TIA. Appreciate your experiences

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Do yourself a favor and don't overthink it.  Purchase bulk ac cable, ac power plugs, and iec plugs from reputable manufacturers like Furutech, Neotech, or DH Labs and then carefully construct the cables by attaching the plugs/iecs and connecting the wires and shielding.  Some like PCs with shielding for front end/digital components but not for power amps.  IME, shielding is never a bad thing and most of the already constructed power cables available are shielded.  I have had good luck with both Furutech and Neotech bulk ac cables but if you check the links you will see a couple of the Neotech offerings use UP-OCC copper, which is no longer made.

Regarding your "panel to stereo" circuit, at a minimum, dedicate that circuit for use only by the stereo.  Beyond that it comes down to personal preferences and how far you want to go.  I have separate dedicated circuits for digital, front end preamplifiers, and a third totally separate circuit for my power amps.  Each circuit is 20A and uses oversized 10awg wire.  I am sure having three circuits is overkill.  Some will probably tell you a single circuit sounds best.  If you are using a distribution box for your whole system, then you don't need more than a single circuit.  Some add whole house surge protectors, power regenerators, and other stuff.  Good luck.