Please don't expect results from me (OP)...because...
I'm just a dabbler in this hobby. I've tried making some "just for the heck of it" simple projects. I made a set of waveguides using stretchy fabric and (in my case) Gorilla Glue (in solvent) to harden them. Works. Audio quality? Who knows? These were just for fun. And then in about 2015, I had the misfortune to find a cheap used pair of Yorkville Unity that I fixed up and have been happy with since then. The earlier speakers, 3 pairs of Bose 901s, are collecting dust in a room somewhere
Addendum: If I were determined to make a DIY horn/waveguide, other than the "I've got a $100,000 machine and tool shop available and the skills to match" option, which I lack, I would play with the fabric/epoxy or, give a try at least, to using an IKEA lamp shade
Speculation: even if there were slight differences between two waveguides, if they were used with DSP/custom EQ per channel, I wager they would.sound (not to say measure) identical. At least acceptable. I mean, damn it all, I listened to Bose 901s for years and they sounded ok.
While it certainly won't be me, I hereby request that somebody work on the idea. IKEA is selling a Bluetooth speaker that is also a lamp, so let us turn one of their lamp shades into a speaker.