Depending what you are doing, say glassing a hull on a surface ship, I use light weight cloth .5oz to 4oz,and epoxy-- finishing resin-- rather than polyester resin. I like the sanding quality of the epoxy over the polyester and the smell is less noticable. You can build up layers of cloth/resin if need be, and heavier cloth could be used, depending on the application.
Great Planes, Zapp, and others make a slow setting finishing resin/epoxy for doing this type of work. Another supplier is West Systems- full size boat supplier-- that you can choose what type of hardner and epoxy you need.
When applying the glass ,I usually coat the wood and squeege resin through the the cloth after placing it on the model. I try to remove as much of the eccess resin as I can at first, then recoat after the first coat cures, sanding between coats.
Hope this helps