More than one
From a guy building a composite airplane, use more than one layer of cloth.
If just looking for cosmetics and not lots of strength -
If you can find some 1.7oz or 2oz cloth, use it, cut it on the 45's (bidirectional) and use 2 or 3 layers
If looking for strength, you'll have to use 4-6oz cloth, I can't remember all the sizes. You want something that has a pretty tight weave and use at least 2 layers (BID's as they call them and cut them also on the 45's). This is the easiest way to work the glass and it gives the best strength in length and width. UNI (cut on the 90's) only give strength in one direction (lengthwise I think).
Another trick is to mix your Micro with some FLOX in it. I always mix my epoxy and flox to a syrup, maybe a little thicker before I add my Micro. You'll also need to do this over your build up area, so you can create a "smooth" surface for your cloth. Even the edges, where the cloth lays down on old fiberglass, make a radius out of the Flox Micro mix, then lay your cloth down over it. You don't need to wait for the Micro/Flox to cure, just mix it to peanut butter consistancy and lay the wet cloth down over it. Then roll out all the air bubbles.
I'll assume you know all the sand, clean, wet out, layup, roll out, peel-ply routine...
