I like to ride to and from work on a sporty mountain bike. Naturally to save weight, it did not come with any sort of guard to prevent calves or pants from being caught on the chainring. I like my pants to be clean and unholed, so I decided to make a 3D-printed guard since no commercially-made ones seem to be sold for it.
The chainring has four equally-spaced M5 threaded holes for mounting. The easiest way to find the center position of these holes was to find the inner and outer diameters of two opposite holes. After this, the next most important dimenions are the inner chain diameter, the outer chain diameter, and the flare. For me, the easiest way to measure inner and outer chain diameter was relative to the already-measured screw holes. The limiting dimension for the flare isn't the chain itself, but rather the front derailleur, which can rub on the flange if it isn't well-sized.
I wrote an OpenSCAD model you can find here. I made it to be fully parametric with the exception of some hardcoded tolerances, so I hope you find it useful even if your chainring is not the same as mine.