First I must state that I am no expert, so maybe I shouldn't even be posting here, but as naturals are all I make and shoot anymore perhaps I can help.
First, I cut my forks at least 1 1/2 inches/ 3.8 cm long and allow them to naturally season for at least six months. I hardly ever cut green wood but I know six months is a safe time for green wood. I have an entire room of my shop devoted to natural fork drying where they are exposed to the natural ambient temperature. There are a lot of people who swear by the microwave method and perhaps this is good for you. I personally don't use it but that doesn't mean it isn't good.
I use a folding wood saw both in the field and shop to cut my forks down to size. This makes a clean, straight cut.
I measure my naturals while holding them in my hand. I prefer the base to be exactly even with the bottom of my hand and the fork tips about 3/4 inch/1.9 cm minimum up to 1.5 in/3.1 cm above the tops of where my fingers rest. Keep in mind I use the fork-supported hold so I am actually converting the forks into part of the grip. This makes the handle portion much smaller and allows a larger, wider fork (easier, and safer to shoot) all in a smaller slingshot. Hammer grip dicatates a larger grip. It's completely up to you.
The only tools I use in making a natural are a good sharp pocketknife, folding saw, and sandpaper. That's all you need. Harpersgrace gets extra points for the simplicity of using rocks and old keys. That should show you don't need a full shop to turn out something that can shoot with the best of them.
Some trees have bark that will strip off easily or perhaps after being started with a pocketknife. Here in the American South the two that come to mind are hickory and white oak. Once they are perfectly dried these barks rip right off, saving much pocketknife work. And remember, the more you touch the fork with the pocketknife, the more sandpaper you are going to need.
Once you have debarked it, use the pocketknife to round off the fork tips and base of the grip. I spend a lot of time getting these right as the fork tips will eat your bands and the grip base will eat your leg as it rides in your pocket. Take your time with the base especially, for it is a focal point of your catty. The fork tips don't have to be absolutey perfect if you are going gypsy tabs but they should be smooth and have no sharp edges. Also use your knife CAREFULLY to lower the knots, but don't get completely rid of them. Leave them slightly raised. When you sand you'll expose beautiful grain in them that will become a focal point of your slingshot.
Once you've gotten all this done begin sanding with medium sandpaper. I spend hours sanding every slingshot I make to get them nice and smooth. When you get tired of sanding remember you will be judged by the product you turn out. Take a break and then sand more. When you think you are done, sand some more. And when you do finally finish, sand more. When you truly do finish the medium paper, go over it for a bit with the fine paper to get rid of any scratches the medium left.
Now you add your attachment point, be it notches, holes, or the tabs. Your choice here.
Once you have done all this, you must now attempt to break the fork with your hands. I don't jump/stand on them but I do my very utmost to break them with combined hand and arm strength. If I am going to pull elastics attached to this I need to have some trust. When a fork breaks off you know it's coming for your face. So do your best!
When it's passed the torture test apply your stain or varnish. I prefer a natural stain to let the wood speak for itself but again this is your natural and therefore you should express yourself as needed.
I made all the naturals below except for the lower right, which was made by Dayhiker. You should spend some time studying the attention to detail and skill he showed in his fork tips as this is an over-the-top flatband slingshot. He did a perfect job on this one. I believe it also was a microwave-dried one, which I am not a huge fan of but the wood is perfectly stable with no cracking. So he's on to something there.
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