Greenhouse orientation should be considered together with sun path, prevailing wind, slope, surrounding shade, drainage and the internal crop layout.
There is no single orientation rule that overrides every site condition. A narrow hill plot, strong local wind or nearby structures can change the practical choice.
Leave room for water storage, filtration, service access, crop handling and future maintenance. Drainage around the greenhouse should prevent outside runoff from becoming an internal production problem.
For larger structures, create a simple site plan before ordering material. It helps coordinate structure, irrigation, access paths and utility locations.