It depends on what the mask is to do - if it is a contrast reducing mask, then it likely needs to be Pan. There was a good aritcle pair a few years ago in Photo Techniques that discussed calibrating your process - exposure under the enlarger as a light source, and calibration of a standard development tiem to get the required contrast index of the mask.
To date, I have not gone to the length of pan mask making; usually I just do it using lith film, and do it to make either unsharp masks or hard masks for inserting areas of text for posters, etc.