There are no nice sounding DIY designs.
If there were then I know exactly the guy who would have them. He’s spent the better part of 40 years building all kinds of interconnects, speaker cables, and power cords. He’s built every design out there. He’s torn apart and copied enough big money name brand wire to do ten systems five times over.
He has yet to build anything even close to the first cheap (under $200) interconnects and power cords I was buying 20 years ago.
Its a complicated subject made even more difficult by there being so many poorly made yet professionally designed and very expensive products out there. But the reality is that whatever time and money you have to put into it will be much better spent auditioning (not asking, not reading, but listening) and then spending whatever you planned on spending anyway on whatever you find sounds best.
That's based not only on the scores of tries he made, but everyone else I know, including a few times I let myself get deluded enough to think I’d found the answer.
The one exception is if instead of being focused on obtaining the best sound for the money what you really want is to be able to say you made it yourself. In that case, as Rosanne Rosanna-Danna used to say, "Oh. Well, that’s different then. Never mind!"