Randy and Graham I got lucky in the location search for this round house from the steam era.
It belonged to the Pennsylvania Rail Road in Crestline (or Mingo) Ohio. I believe it was the furthest west that the PRR ran. It was sadly torn down in 2006 and like much of railway history its just gone. Well sort of, the foot print remains. However on the plus side it is believed that some of the engines pictured may have survived and are preserved static locomotives.
@mark sennuck although they appear to be closed at the moment there are a number of historical railway organizations in St. Thomas, Ontario. Wonder if they might be able to make a suggestion on somewhere you could volunteer to work on these projects.