I have a (yacf) buff. And another buff (winter mode) and I've repurposed a couple of shirts (it's OK, they were already in the rag bag - does anyone else have a rag bag any more?).
I used the govt approved 15cm x 25 cm design instructions.
One is 2-layer and ties, the other 3-layer, with elastic - simply because of what I dug out of my box of haberdashery stuff (like your box/pile of random cycle bits, only with zips/buttons/ribbons/elastic/etc). I may do a plain one if the fancy ever takes me but 3 can be rotated daily if it comes to it. Though I try to avoid shops in general anyway.
& no, I haven't worked out how to stop glasses misting up. Luckily I don't use them for close up, which tends to be when I need to speak.