Could be predator proof depending on what the walls are made of. I'm building sort of a solarium for a winter run to take advantage of that light and warmth using cattle panels with hardware cloth then transparent roofing panels. It will need careful shading in summer to avoid pre cooking your chicken!
Under construction now is my greenhouse/coop. Total footprint is 16x48. It will have one adjoining wall with a small woodstove on it, I'm putting the water and food on that wall in the coop, hoping to keep it all from freezing.
It will have screen instead of insulation for the summer.
You will have to be really careful if you are using a straight up greenhouse for coop. It can get awfully hot in there even in the depths of winter, making them vulnerable to sudden deep freezes. You will have to modify it so that you have extra good ventilation even in the winter.
In the summer, you will have to lessen the solar gain. Put a tarp over the top, train vines up and over, use outside curtains on the front windows. If you don't, and don't have great ventilation, you will indeed have precooked chickens.
My green house spikes temps well over 100*F on a regular basis, even with both end windows wide open. I would not advise it.
However, I have plastic covering 3 walls of one bay of my chicken run, with a green house tarp over one portion of that area to make a winter sunroom. This works well, but I must take the plastic down from the walls by the end of April so it does not cook the birds!
Personally, my thoughts on this was if you could use the frame as a base and go from there. I wasn't thinking of using the actual greenhouse materials. This morning I saw a greenhouse frame beside a house and thought, "hmmm could be a chicken run".
My experience is you can turn just about anything into a chicken coop/run. I have a duck house that is just spare pallets nailed together with hardware cloth and extra roofing materials up top. They love it. My coop is a shed. If it's a building, I guarantee you something will be happy to call it home.