Building a model sailboat takes patience, skill and experience. For novices, modifying or repairing an existing model is the best and first step to make when getting into remote control sailboats. Rigging an existing model gives you room to improve on the design to produce a faster and more advanced sailboat.
Replace the existing sails. Measure the old main sail and head sail from the model and cut out the new ones using Dacron but add one half inch on each side.
Fold over 1/2 inch of the material and hem it using a sewing machine and polyester thread number V46 or V69. Use a white or off white color to hide the hem. This will prevent the sails from fraying.
Add grommets to each corner of the sails 1/2 inch from the edge. Fasten them into the corners by placing one half on the front of the sail and the other half on the opposite side and pinching together with a pair of pliers until the two pieces snap together. Cut out the sail in the center with a utility knife.
Attach the mainsail to the eye bolt positioned at the bottom of the mast and the aft end of the boom. Thread spectra fishing line through the grommets and loop it through the eye bolt to secure the sail. Do the same at the top of the sail and the top of the mast.
Attach the headsail to the top of the mast in front of the mainsail using the spectra fishing line and looping it through the grommet and the eyebolt. The headsail is then secured to another, shorter boom that has the front end attached to the bow of the boat. Run spectra line through the grommets on the bottom of the sail to the front and back eye bolts on the short boom.
Spectra is strong and when under tension, it can cut into the hull or plastic components so add a sleeve made out of Dacron where the lines rub against any parts.
Ask sail makers for scraps or material or to provide you with old, torn sails that you can use to make the remote control boat sails.
Stay away from more complicated rigs such as double mast designs or using spinnakers until you are experienced with the hobby since these rigs are require more work to rig and are harder to control with a remote.