You can get Elmer's fiberglass cloth and resin at Lowe's. It's the same people that make the glue, so it's a name you can trust. I recently repaired a large crack on the interior of my boat with it. I wouldn't buy the "fiberglass repair kit," as it's too expensive for the little bit they give you. The resin comes with a tube of hardener. Definitely practice on a piece of wood or something first, 'cause it's extremely messy to work with. Once you mix the hardener with the resin, you've got about 10 minutes to get it the way you want it. The best approach is to just mix a small amount at a time. After it hardens, you can sand it down and paint it. Plan on discarding any materials you use such as brushes, and I would also recommend throwing away whatever clothes you wear. Those tiny little fibers get in there and just don't come out, so you won't want to wash them with your other clothes, trust me. WEAR GLOVES! Not only will the fibers get in your skin and be there virtually forever, but that resin will blister you!
Good Luck