John has the right and perfect way to do it.
1- You need a hammer and a Dolly, various hammer/dolly for various shapes.
2- You can d draw your exact piece in paper/cardboard, cut the paper when you have to stretch the metal and fold it where you have to shrink ( accordion style) the metal.
3- Now you know where to hammer your metal, relax drink a beer and think about your work.
4- Warm your metal just a little, it will become less stiff. Hammer your metal until desired shape. Have fun.
5- Sit down and watch what you have accomplished.
Depending of the type and thickness of metal, it will be easier or harder to shape. If you are looking for a perfect work of art, let someone else do it, If you will be satisfied with little less than perfect, go, try it out and have fun.
Metal work it so much fun!!
Dayz