When you are making a hypertufa container then you will want to make sure that your project will actually be usable when you get done.
Choose a mold that fits whatever shape you desire. Start off with the bottom of your container first and then work your way up to the walls. You may also want to use a box or bowl that will go on the inside of your hypertufa container to help shape the inside of the container.
Most of the time you will be using these containers outside so there is something very important that you will not want to forget. Put drain holes in the bottom. You can use some small pieces of pipe or just about anything else that is round so that you can put uniform holes in the bottom while you are building your container. Forgetting to do this makes a very good place for mosquitoes to live after it rains.
You may also want to add some nylon fiber mesh to your hypertufa mixture to add to the strength a little bit. This will help make the walls of your container more sturdy as well.
Usually about 1.5 inches thick for your walls are good enough but remember that if you are making a tall container you will probably need to increase the thickness of your walls for some added strength.