Below is an explanation for pre-treating a house for termite protection, but the same method applies to a shed, outhouse, or any type of building. If you are not pouring a slab as the bottom of the shed, then you would still treat wherever you are going to have the shed touch the ground.
When building a house, you would want to perform a pre-treat before the slab is poured. A pre-treat is done after everything is prepared for the slab to be poured other than placing down plastic, but before the concrete is actually poured. You should treat all ground before any slabs are poured, including any porch, patio, garage, and other slabs in addition to your main foundation slab. When applying a pre-treat, you should apply 1 gallon of solution per 10 square feet. So if your main slab is 1500 square feet, then you should apply 150 gallons of solution evenly over the slab area.
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After you have treated under the slab and the house is finished and all grade has been pushed up against the house and landscaping installed, you should perform an outside trench and treat as the last part of the treatment. This will protect any new termites from entering around the outside of the structure. This procedure is outlined in our How To Do A Termite Treatment Article: http://www.domyownpestcontrol.com/termite-treatment-c-3_352.html