Grange Barn in Coggeshall in Essex is one of the oldest agricultural buildings in Europe. The oldest timbers in the building date from the early 12th century.
It is a huge building – 120 feet long, 45 feet wide and 35 feet high
It was built by Cisterian monks so that they could store their agricultural produce
To me it is one of the wonders of Britain and clearly shows how important the management of woodlands was in the 12th century in producing timber for huge buildings like this
The building was used for agricultural storage up to the 1960s
After which it fell into disrepair – during the early 1980s it was saved from destruction and restored by local people – I first visited Grange Barn in 1986 with Oliver Rackham
The roof consists of over 85,000 tiles
The Barn was given to the National Trust in 1989 and is now open to the public – see here for the opening time details.
A Dartmoor blog 
Strata Florida abbey near Tregaron was built at a similar time. Worth a visit! Fairfax