With the winds we are getting now i think its not so much of where you are going to put it its more like how are you going to keep it.
If you are going to put up an aluminium greenhouse then do it properly from the begging, it will save you heartache later.
Spend a little bit of dish dosh and get some breeze blocks, sand and cement and build your base up at least two courses. Not only screw the base of the greenhouse to the blocks bracket it as well. Doing it this way you are gaining extra height so therefor more shelving space.
If you think that's a bit expensive to do it that way consider the cost of replacing glass compared to the price of the blocks, sand and cement.