Almost every state and local municipality has adopted the International Building Code. Under the IBC no permit is needed for a shed your size. Check with you local code official and if he say it does need a permit ask him to show you the shed exemption and ask him to explain why it does not apply to you. Even if a permit is not needed, do something to hold it into the ground to avoid having a flying object in a major storm.
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You may or may not need a permit, but you do need to be careful about where you site the structure. Make sure that the site is in compliance with the Massachusetts Wetlands Act and that it is COMPLETELY on YOUR property. Always check with the folks at Town Hall first before starting construction.
Yes, a shed of that size will likely require a building permit. The Building Code excludes from its requirements buildings that are 120 square feet, or less. a 12x12 structure exceeds that requirement. Also, there are more regulations that need to be considered than just the building code.
The local building inspector should be consulted early in the process. The building inspector will inform you if a building permit is required, and will also likely apprise you of other local bylaws/ordinances that are implicated and require compliance (set backs, etc.)
If you disagree with the building inspector, there is an appeal process with short, strict deadlines.
DISCLAIMER: This answer is provided in response to a "hypothetical" question and provided for general, informational purposes and does not create an attorney/client relationship. The information presented is not legal advice and may change based additional information and research. It is recommended that you speak to an attorney to discuss your specific legal issues.