I just completed a pair of mittens made from two layer goretex fabric.

I purchased the fabric from Quest Outfitters (www.questoutfitters.com)

I really like the eVent rain mitts sold by MLD but did not want to pay $40.

I used a pattern that I found at thru-hiker.com. The pattern was for fleece gloves but I figured it would work with goretex as well.

The final weight for the pair of mittens was 0.8 oz according to the scale at my local post office.

I was able to purchase a half yard of 2 layer ripstop goretex fabric for only $5.

Nice. Can I make two suggestions?
Add a bit of light webbing and velcro at the back of the wrist to help keep them on.
Add a light drawcord at the hem to keep (some!) of the rain/snow out - especially snow. Nothing keeps all the rain out.

I do this with PU-proofed 70 denier nylon, and they work fine.

Another suggestion, based on previous failures.

Patterns designed for stretchy fabric do not work well with non-stretchy fabric, for the obvious reasons. I once made rain pants using a sweat-pants pattern, and it sure felt funny while walking in them!

Be sure to cut generously wherever the item is supposed to move, stretch, or otherwise conform to a moving body part.