I expect there was a steam engine when the place was first built, even if it was swapped for a diesel engine later.
If there was a steam engine, you should be able to see at least a brick base for the boiler. It might be a little away from the shop because of fire risk.
The roof trusses are interesting, King-post trusses fabricated from flat boards. I've never seen that before, though it might be common round there.
Andy