Why do you want a mask? To change your features to create your character? To disguise your identity? To make a quick change?
Is more than one person going to be wearing this mask?
How much time will you have for putting it on and in what circumstances?
Does the mask need to be flexible or ridged?
How greatly you are changing the physical shape of your face? This will greatly impact what type of materials you need to make your mask from.
What sort of activities are you going to be doing in this mask? Standing still, walking and talking, singing and story telling, dancing, cartwheels…
What do you need for comfort?
Does your face get hot easily?
Vision? Do you need to wear glasses under or over it?
Do you or the people you are with have allergies that need to be taken into consideration.
How durable does your mask need to be? Do you intend to make an entrance and then be done? Do you intend to use this mask over and over in the future?
What materials will you be able to use?
What skills to you posses, or NOT posses? Sculpting, sewing, painting details?
How much time do you have at your disposal to create the mask?
How will you manage the Balance (keeping it from tipping one way or the other)?
How will you keep it on your head?