Asking for a friend who'd like to do something and has the tools and materials but limited design skills.
1. https://www.dezeen.com/2020/04/09/apple-coronavirus-face-shield/
2. https://www.designboom.com/design/engineers-hack-scuba-masks-to-use-as-ventilators-03-26-2020/
https://www.youtube.com/watch?v=aNjpH5lBZ8w
go to around 1:09 in the video seems to me very practical if one wears glasses, otherwise one could use a similar approach with el-cheapo protective glasses or "over glasses" safety glasses.
From experience with wearing "magnifying lenses" for little works with high precision like these:
https://rukminim1.flixcart.com/image/832/832/magnifier/a/h/n...
the front strap is very uncomfortable/sweaty, so the issue, besides the design (and making DIY one similar to Apple's one but with more standard round holes is easy) is with the material that must be anallergic and prevent or absorb sweat.
Note that to make them actually comfortable you'll need button hole elastic as well as foam padding (I used 1/2 inch by 1/4 inch foam window seal). This design is superior to the Prusa and Apple ones because it adds additional protection at the top to keep particles from floating down onto your face. It takes longer to print, though, so the Prusa people don't like it as much.
A few other notes:
The face shield shortage is disappearing pretty quickly in the US. From conversations with a few healthcare workers, it sounds like there won't be much of a shortage for these by the end of the month. What they really need are surgical-grade N95 masks and certified ventilators.
Please don't try to make DIY ventilators. See [2] for an explanation of why a lot of these well-meaning projects do more harm than good.
Another thing that's easy to make are surgical mask strap extenders to go behind your head so your ears aren't constantly strained by the elastic. Example in [3]. I gave these to a few healthcare workers who requested them. Personally, I don't think they actually work that well on the mask I have without using hair pins to hold them in place (they should really have a rubberized coating to keep them from sliding down your head), but they're still better than nothing.
[1] https://3dprint.nih.gov/discover/3dpx-013359
