Answer: On first thought, I would say to have your greenhouse window face south, to maximize sun exposure. However, the amount of sun you want will depend on what you are growing, the type of glazing you are using, whether you plan to use the area as a sitting room (and want to have a particular view) and so on. A large, south-facing window (especially a greenhouse type with a glass ceiling) can let in a lot of heat--great in the winter, but overpowering in the summer. You'll want to plan for sturdy shades and adequate ventilation.
It sounds like a large and expensive project; you may want to hire an architect/designer to help you make the most of it.
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