Measure and stake out a flat area where you wish to build your root cellar.
Lay pavers in straight lines around the edges of your staked area. Leave an opening for the door. The pavers will serve as the foundation for the cellar.
Build walls on the foundation with hay bales. Stagger each layer for extra stability.
When you have built the walls to your desired height, place a sheet of plywood followed by a sheet of metal on the top to serve as a roof.
Mix clay, sand, water and straw together in a bucket to form a cobb mixture with a glue-like consistency.
Put gloves on to protect your hands.
Apply a layer of cobb, using your hands, over each wall of the root cellar. Start at the bottom of each wall and work your way up until all the straw is covered. Let dry.
Place shelves inside the root cellar, if desired.