I can see a few problems. One. Piano hinges are very expensive. And how would you seal them? Would you use the automatic roof vents on these also? You would need something to hold them closed. You could seal with foam tape just where the pieces meet.
How big is the greenhouse going to be.
It maybe best to use two or three regular size vents on the roof and one large exhaust fan on the side that is exposed.
Or you could use one or two attic exhaust fans on the top and motorized shutters at the end and the corner.
It would be helpful to have more information.
Zone Hi's and low's. How much wind do you get and the size of the greenhouse. What you intend to build it of, Etc.
Your idea could work. But if you intend to use this as your only ventilation without exhaust fans and shutters it will not cool it very well.

Here is a link that might be useful: Natural ventilation

The greenhouse will be 20'x 8', using 8mm double wall polycarbonate sheets. The roof slope will only be 4:8. My husband has suggested that we might make the roof vent 8' long x 2', and have two 2'x 4' vents on the S wall with fans. We have only occasional temps into the 80's, but in the greenhouse it exceeds 100 in a hurry. The prevailing winds when it's nice come fron the WNW, and that side is partially blocked by an extending wall on the N side of the greenhouse. I'll be using it primarily as a season extender and to grow herbs and tomatoes during the summer which averages tepms in the 50's - 60's, and 7 - 8" of monthly rainfall.

Thanks for your input.

If you have vents on the same wall as your fan I don't think it will draw the air through the roof. Fans and vents should be opposite eachother.
Would love to have your rainfall.

Thanks for the graphic. I was thinking if I put the fans by the lower openings, I would set them to draw the cooler air in, assuming it would pressurize and draw the hot air out of the roof vents. But not having the experience, maybe this isn't how it would really work. Maybe I should just set the fans to get the air circulating and let convection take care of the venting. What do you think?

This might help....

Here is a link that might be useful: Climate control in a greenhouse