When putting up a polytunnel it says put it up east to west , does this mean the ends with the doors should be east west or the long sides ?
Running the ridge of a greenhouse east-west offers the long side of the house to the sun and this generates more heat. However, if tall plants are put on the sunny side, they may shade others. But then again this might be a good thing. Running the ridge north south allows even light in both sides.
These considerations are not critical and usually a greenhouse is placed whenever convenient.
More on this: https://gardenie.wpengine.com/gerrycategory/siting-a-greenhouse/?id=5488