My advice is have a look in the back of Classic and Sportscar magazine.
I had one put up 15 years ago in Somerset and on my visit last October it still looked good.
Mine was a 24 foot square garage workshop with barn doors and looked nice with a felt tiled roof all erected in one day by two guys from the manufacturer from Warwick.
The joy of timber no damp/humidity.
Looked nice at the bottom of the back garden too.