Pattern for N95 mask: https://www.makethemasks.com/
The CDC: https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/diy-cloth-face-coverings.html
This site has several other sets of instructions to make masks so if this one won’t work for you try checking this site for alternatives.
NIH Collection of 3D Print Instruction Sets for face masks and shields including how to assemble and wear: https://3dprint.nih.gov/collections/covid-19-response
Simple no-sew mask:
The original blog with these instructions: