When building a shed, it sometimes helps to have wood on hand. But not all sheds are made out of wood! Some sheds may be made out of old tires laid on their sides and filled with compressed dirt, stacked up like large round bricks!
A soil compacter is necessary for this kind of construction: simply filling the tires won’t do. You must pound it in until the soil is hard as rock! Then, the tires actually are pressed together and the soil acts like a kind of mortar.
Tires are largely non-toxic, but not good for growing in. The plant roots will touch the tires and eat them, giving you poison. But unless you are eating the tires, you will not likely be poisoned by a shed made of them. They make good animal pens for the same reason! They leach almost nothing into the ground if stacked above it and the leaching when buried does not go very far.
Consider the other materials you can use to build a shed and you’ll find wood is only the beginning!