I just checked Ravelry (fiber arts website), there are 32 crochet patterns with the tag “face mask” but only one looks like an actual face mask - most of the others are ear savers. The pattern is free but is meant to be a costume piece. I don’t have actual crochet advice (I’m better with knitting) but there is a base pattern out there if you’re on Ravelry.
in terms of the masks I’ve been using/making, I’ve found the masks with ties are easier than the ones with ear loops. The ear loops mess with my glasses, are either too tick to fit behind me ears or too thin to be comfortable, constantly snap off my face... as someone who isn’t used to masks, it's more pain than it’s worth (but I gotta wear them at work).
the pattern I’ve mostly settled on for sewing masks has 16 inch ties off each corner (I think
@dibbles posted the pattern). It’s more than enough for adults with varying sized heads to use and tie on comfortably. I believe the mask size ends up a total of 4”x8“ (when “scrunched”) and fits perfectly on me. I might make a few a bit larger for my husband’s bigger head+beard.
I was considering knitting a few masks with spaces for filters. My plan was fingering yarn with a US4 needle (3.5mm). I know that doesn’t translate well into crochet but I think needle/hook sizes are similar. I have to clear up a few works in progress first, then I’ll consider masks.
most threads I’ve seen talk about the masks themselves not the filters. My dad recommended a furnace filter that’s rated to catch bacteria, allergens, and viruses - it’s almost the same as the material n95 masks are made out of and you get A LOT for under $20. I just tore off the cardboard and stretched it out, I think you can easily cut 20+ filters from it (I’ve cut 2 so far). My work is having us reuse filters daily but wash the outer cloth mask. A single family should be able to use one furnace filter for a good while before having to worry. Before I got my furnace filter I picked up a box of i scented swiffer cloths, my theory was that it would catch the allergens and pollen so we could cut down the seasonal issues and not mistake them for COVID.