Select two roses that you want to cross-pollenate. The blooms should not be too tight, perhaps about one-half to 3/4 open. Carefully peel off all the petals. The rose stamens inside should look golden yellow and fresh. With sterile tweezers or cuticle scissors, carefully remove all the stamens at the base of the rose hip, so you do not damage the pollen sacs (anthers). Place the rose stamens into separate, clean film canisters, and place the canisters in a dry place, but not in direct sunlight.
There will be disappointments along the way, when many rose seeds fail to germinate, or perhaps they do germinate, only to die several weeks later from damp-off disease. Sometimes a rose seedling will turn out to be as ugly as sin, or very sickly, and you will reluctantly have to throw it away. Other times they will be just ho-hum, or look too much like its parent, and therefore have no value. But, just when you don't expect it, you might discover that one of your rose seedlings turns out to be very special.