The location and orientation of a structure are two different things that need to be given careful thought to since the consequences are so long lasting. The cost of making changes after the fact are significant and often make it impossible. You should never put a structure somewhere simply because the area is not good for anything else. Location is more about what you need and orientation has to do with what the structure needs to perform well.
Location has to do with accessibility to power, water and handling the product that the structure shelters. If bringing in water, electricity or a driveway is too costly for the budget at present, you will have to start weighing cost versus benefit. This can only be accurately done if you understand the requirements, choices and consequences. Drainage, ventilation and light requirements are also important considerations which change from location to location.
Orientation has to do with a structure being north/south, east/west, or somewhere in between. This will have an impact on ventilation, light, snow shedding and lay of the land. For all of these things you need to have a good handle on what the structure needs to perform well. A structure must be level from side to side to shed snow well but can have some slope from end to end. Ventilation is easier when a structure is inline with the prevailing winds but you do get more sunshine in the building if it is north/south.
Check out the presentation video and the rest of the series Norm spoke on Greenhouses 101 here. Stay tuned for the end of January 2016 when he presents Greenhouses 202!