1) Add-on 2) Addition 3) Annex 4) Extension 5) Extension to a building 6) Improver 7) Supplementary building 8) Wing 1) Adjunct 2) Annex 3) Ell 4) Lean-to 
A framed tent structure which can be attached to a motorhome and left as a free-standing unit in its own right if you drive away
An annexe or annex is an extension to a main building. Typically an additional room constructed after the main building has been completed. In America and Canada an annexe is also known as an addition.