What's the biggest summer house you can put up in need planning say-so? ...
well, if you are caught later they will red tag and condemn your property. It is other good to database a building permit anyway for your safekeeping. Only some requires the planning departments permission. It is so you hold someone next to you that wishes to paint his house deep purple and you enjoy to look at it. I would least ask the county what the requirements are.
It's going to depend on who governs the topography. Example, I am on a farm outside city precincts but in a county. I enjoy built 2500 sq ft house, a barn, a workshop. There are no restrictions EXCEPT, the county sets to conditions for sewage, or septic tanks, as to how voluminous a system is required to accommodate the number of individuals living in the house.
So check beside who governs the ground use, city, county, parish, state Etc.
Answers: As long as you dont put down permanent foundations, as big as you resembling!