You need a suitable plot with enough space to allow access to the growing stool from all sides, and three young saplings (known as "whips") of a suitable species such as Sycamore.The easily assembled plywood jig, or drawings from which you can cut your own,is available . For further details please email:
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It comes flat packed, complete with instructions.
Accurate planting of the saplings is easy with the help of the positioning guide, supplied with the kit.
They are trained to shape as they grow, being held in place temporarily with plant ties. 
When thick enough, the saplings can be gratfted together to form the joints of the stool frame 
The jig top panel keeps the horizontal sections of the sapling flat and correctly spaced.
In about five years the frame should be sufficiently robust to allow you to harvest it and to add the top of your choice.