If you design your own stuffed animal, you would have total freedom in the way you can create the toy. It all comes down to the pattern you will design.
So first start with a piece of paper and a pencil. You should already have an idea of the stuffed animal you want to make. For example a teddy bear or a cat. If this is your first stuffed animal you design yourself, it would be better for you to start with an easier and more classic shape. Not a lion for example.
Have a general idea in your mind of what you want to draw. Also keep in mind the approximate size of the future toy. You will have to draw the needed pieces separate from each other. So if you need a basic idea of the needed pieces, first you can draw how the finished stuffed animal would look. You don’t need to draw it absolutely precise, just have an idea.
Then draw the basic pieces you will need. Start with the bigger and easier pieces like the body and legs, tail. Stuffies are often made out of two identical pieces, like the legs for example.
Try not to rush and keep in mind that this may take some trial and error. It is quite likely that you will have to redo a few pieces until you get them just the way you envisioned. But that is quite normal, so don’t feel like ou are doing something wrong if you have to redo something a few times.
This means that you would need a little bit more fabric than usual, so that you have enough in case of redos. Use pins to attach the pieces together in the test fitting phase.
After you are satisfied it is time to sew the pieces together. Follow the usual method. Take two pieces for each part and place them with their outer sides towards each other. Remember to allow about a centimeter or two extra on the sides of each piece for the stitching.
Then sew the pieces together and leave one side unsewn. Use it to turn the ready piece inside out and then fill it with stuffing. Depending on your design you may now sew the ready part closed or sew it closed with the rest of the ready parts you have.
Keep in mind the toy can and probably will look different when you stuff it. So be ready to make more adjustments if needed.
If you really like the finished product, retrace the original pattern pieces on a piece of paper to have them saved for future builds. Or you can share it with friends and with the internet.