It would be best if you own all the acres, because on the planning application you would need to prove what land you own (Hence the question at the end, do you own all of the land, if not, who does). Do you really think a local council would let you build a barn on one acre and then rent the other 11 or so... Just for you to stop renting them in a year or so... Yes they would make you take it down, because you could only build the barn under permitted development, all they would do is add a condition which states once you fail to rent 11 acres or so the barn has to be removed (If they allowed you to build it in the first place, which they wouldnt), more to the point what about the guy who owns the 11 acres you are renting ?? dont you think they may also have a barn on their farm which was allowed under the permitted development rights on the land you rented ?? and therefore because you have informed the council you now rent the land, the owner would have to remove their barn because they no longer have use of the land !!
In an ideal world you would buy 12 acres or so, build a barn and then rent out the rest of the land you no longer need, keeping the barn and afew acres for yourself. But you still wouldnt have permission to live on it.
If anyone has any questions about this, I will do my best to answer on
[email protected]. I hold degrees in architecture and planning for the UK and have my own land with which I went through the same situtation as most of the others on this site.