According to the Yorkshire Dales National Park Authority (YDNPA), in 2014 Andrew Avison constructed the building to replace one which had burnt down, without applying for planning consent.
At nearly 13 metres to the ridge of the roof, the new building was nearly five metres taller than one it replaced, and was so prominent it had becme known locally as the "giraffe house", the park authority said.
An enforcement notice issued by the YDNPA required the structure, at Middlefields Farm, Melmerby, to be demolished or reduced to the same height as the building it had replaced.
A planning application was submitted retrospectively, but was refused because the height, bulk, materials and siting of the building was detrimental to the quality of the landscape.
Two appeals - one against the refusal of planning permission and one against the enforcement notice - were then dismissed by a planning inspector.
According to the park authority, Northallerton Magistrates’ Court yesterday fined Andrew Avison £750 and ordered him to pay legal costs of £1,000 and a surcharge of £75.
Yorkshire Dales National Park Authority chairman, Carl Lis, said: "Today’s court proceedings do not affect the status of the enforcement notice. It still stands, and I urge Mr Avison to take action to reduce the height of the shed.
"If Mr Avison does nothing, the authority can either take further action through the courts, or employ a contractor to demolish the building – and send him the bill".
Lis added that during the course of yesterday’s proceedings, Avison alleged that a senior planning officer approached him seeking a bribe. He also alleged that two members of the authority were complicit in this.
Lis said that Avison had made the council aware of the allegations earlier this year and the council had "carried out a thorough investigation in response".
Lis said: "This investigation concluded that the allegation was not only scurrilous but malicious. The allegation has caused considerable distress to the officer. It has also cast a shadow on the reputations of two long-serving and well-respected local politicians.
"Mr Avision’s decision today to make his allegation public in court was clearly nothing more than a desperate and ill-advised attempt to try to wriggle out of a simple obligation to comply with national planning laws. Mr Avison has resorted to pure invention and embarrassed himself."