To start with, your root stock is the plant upon which you will graft that seedling so that it will grow and bloom forever after as your seedling. The rootstock most commonly used are either Pride of Hankins or Pink Albo. From my experience, Albo is used more in the Miami area and Pride of Hankins in the balance of the state. I've found that Pride of Hankins can not withstand as much wet feet as Pink Albo.
The best place to get started grafting is to find a ready supply of rootstock in your neighbor's yard, or go to one of your local growers. They always have a couple of missed pots sitting around that they may give you as starters. Plant these plants in the corner of your yard where they will not be seen. This is necessary because neither of these two varieties make for pretty bushes if used for root stock.
When your mother plants get big enough so that you can cut off some ten foot streamers, cut a foot or so above the ground. The growth you have cut should be about 6 feet long. You then can cut this wood into 8-10 inch lengths. Be sure each cut is 1/2 inch below a leaf node.
Now, ask the fellow who you got your starters from how he starts his cuttings. Everyone has their own method and what works for him may not work for you, but start there. I grow my rootstock in 10 inch pots. I put two pots together, twisting them so the drainage holes overlap. Put a piece of paper over the center hole. Fill the pot a little over half full of Perlite. As you were making your cuttings, place them into a large bucket of water with a couple of shots of Miracle Grow Root Starter where they can soak for a couple of hours.
Pull the cuttings out and place on a drying shelf for a few minutes. Put the starting water in the Perlite. Get a jar of rooting hormone and now dip each piece of wood into the hormone and put into the Perlite. Be sure to bury the node. I get about thirty starts a bucket.
Now comes the heartbreaker. Each garden is different. My pots are placed in filtered shade and are sprinkled with water a couple of minutes each morning and mid afternoon. Start new cuttings so that you are going to be home for the first couple of weeks to tend your babies. A downpour every afternoon will cause your starts to dampen off. Too little moisture will slow the starting process and cause damp off.
Now the next important step, removing the rootstock for repotting. My experience is that too many people become impatient and try to remove too soon. My rule of thumb is that if I can lift the whole pot up by grabbing ahold of the longest growth, then it will be ready to transplant in about a week. Place the pots in filtered light, fertilize with a little Milogranite and watch your babies grow.
When can I graft them?
Here, most of us have a tendency to try to graft before the plant is well started. I use the same method to pick out plants ready to graft. Pick up the plants by the tall growth and place on your grafting table. If the plant is too loose, give it another week. Regardless of how careful you are in grafting, you will move the plant around a bit if it is not firmly rooted.
The most common graft used is called the side graft- or veneer graft- rather then going into detail about this graft, I would refer you to Larry Johnson's web site on side grafting.
Tip or Top Grafting
Another common graft is the tip graft- this has become particularlly common with those starting rootstock in cubes in trays and grafting in the trays. For this, those tips of the root stock that you would otherwise be throw away can be used. Leave a couple of extra inches so that you have a solid end. Place these ends in a pot of Perlite just as you did the heavier growth. It will grow in the same manner.
I believe you will find this graft successful. I believe it is not used too much because while the graft takes quickly it is a couple of months later before the plant is ready for sale or to put into the ground.
Today we are finding that more and more of our seedlings will grown on their own root. A la Curt Sinclair- you could graft on the tips of the seedlings you are not going to keep and when the graft takes, pot the planted seedling. I believe this was how many roses are grown by commerical growers.