Building is indeed fun. I’ve made my own power cables, IC’s and speaker cables that I’m now currently using, and have for some time now. My subs are DIY, though I had a pro cabinet maker assembling them for me, and he again had the 13-ply panels CNC cut from another party. The physical DIY part for me here only involved mounting the woofers and cables, but the "real" DIY aspect was the research and eventually honing in on the specific tapped horn design, its tune and proper driver complementation. That took me over a year. My music server is DIY as well (it’s relatively basic, really, and could be tweaked A LOT more to even sweeter sonics, but that’s to be done down the road), and though it may not be classified as DIY per se setting the filter values in the digital cross-over/DSP of my actively configured setup was quite hairy in the beginning and was (still is) very much a learning exercise. It’s hugely rewarding though, and not having the physical components like caps, coils and resistors of passive XO’s makes the tweaking process with a DSP quite easy. You can do several presets with different settings and compare them on the fly from the listening position until landing on the preferred preset. Some 25 years ago I build me (from a kit) a 42W class A power amplifier, and used it for over 10 years. Lovely amp, and at ~$1,000 at the time it was a steal. My very first pair of speakers, the Coral Flat 8 widebanders, were DIY as well. For under $100/pair in the early 80’s those had me smiling to music.
