I was at DSO for seven years. Yes, we were told "You need approval to put in outbuildings."
Point was, as Bigjet has said, no amount of contacting, phoning or even personally visiting DSO HQ would get you any information as to how, who or where to make application for such approval.
I don't know of a single case of anyone getting an actual approval, OR an indication that an approval had been rejected.
So, Mullet head- actually the name says it all....