I too, can be crafty.
White plastic mask
I suggest going to Michael's Arts & Crafts, they usually have 40%-50% off coupons--I got mine for $1-$2. Don't worry if it looks tacky since you're altering it anyway.
Thin, black ribbon
You should be able to buy a spool for about $1
Elmer's clear glue is sufficient, you can buy a bottle for $1
1. Trim mask to desired shape.
Before you trim your mask, I suggest flattening the mask on to a piece of paper and tracing the outline so you have a template to work with. Cut the template out, fold it in half, and draw the shape you want on one of the halves; cut. This will ensure symmetry. If you're happy with your design, take your completed template and lay it on top of your plastic mask; trace it on with a pencil, then trim.
2. Strategically apply layers of lace. This process will be difficult due the curves of the mask--the lace will not lie flat unless you overkill with the glue and actually press the lace down until the glue has semi-dried. Use a paintbrush to apply the glue.
I suggest using lace ribbons because they're a much more manageable than using a sheet of lace; My ribbon was about three inches wide. It took two strips to cover the entire mask. When you glue them on, you'll clearly see the divide between the two strips, but don't worry because you'll layer another two strips across to cover any irregularities. Trim off excess lace. Once all the layers have been applied, paint a couple layers of glue on to further seal in the lace.
3) Strategically align edges with ribbon.
This process will also be very frustrating and time consuming. I used the thinnest ribbon I could find--because it's very thin, it will be very hard to glue on and it will get messy. The uneven texture of the lace will make it difficult for you to secure the ribbon. But you will manage. Once you've successfully aligned the edges of your mask with ribbon, wait for it to dry completely--then seal it in with a couple layers of glue.
4) Make vertical slits on both ends of mask with an X-Acto knife, thread ribbons through (it will be similar to threading a needle); knot. Trim if necessary.
Your ribbons should be about the length of your arm--better too long than too short. I re-threaded my mask 4 times because I kept cutting my ribbons too short and I couldn't tie them around my head.
5) Voila, masquerade mask.
My Approach for a Masquerade
Ok, so some people like to get really dramatic for these kinds of things (which you can, it's up to you)--but I like to keep things clean and simple. For my masquerade ball, I wore minimal eye make up (just eyeliner and mascara)--no eyeshadow because I didn't want my eyes to look hooded and heavy beneath the natural shadows created by my mask (tip: your face gets really warm while wearing the mask, so make sure the makeup you do wear is durable and long lasting, so nothing smudges or melts). I wore a mid-length navy blue, satin tunic dress from BCBG with a black shroud, over a pair of lace leggings and black patent heels. Then I curled my hair into loose waves--and that was that :)
Enjoy, good luck!