I agree with Neo. If you do it right, glass can weigh so little that it's negligible compared to other coverings. I built a plane about 6 months ago that is glassed and then painted with clear polyurethane. I used about 1/2 ounce of resin in total and less than an ounce of paint.

Only the fuselage and fin were glassed though.

This is the plane:

http://www.airfieldmodels.com/my_stik_30.htm