Just make sure that you have it in a shady area during the Summer, and/or prepare to provide fans/cooling fans. I can't tell you how quickly a chicken will die in the heat!!
That said, there are many people who do use a greenhouse for a lot of different animals! Not to mention that it would be very light in the cool during the drabby Winter months, especially in upstate NY! I live in Northeast CT.
Agree with person who says that you will need to use reinforcement IF you do use the greenhouse as a coop.
But, you said that you were good with construction. My suggestion is to save your money from buying a greenhouse, and build an actual building. You can use leftover scraps/repurposed lumber from jobs, and older windows at a minimum cost to you.
Outside pens must have wire at least a foot down in the ground and then bent away from the coop in a L shaped fashion, to keep predators from digging their way in.
I use electric poultry net, from Premier 1 fencing in my outside free-range yard, with netting above, or 1"×2" wire, with bird netting above, in permanent outdoor enclosures. And, I now have a livestock guardian dog to protect the poultry.
Even with safeguards in place, a hungry predator will find a way. You just need to deter them as much as possible!! I've lost birds to a mangy/healthy foxes, coyotes, Fishercats, and birds of prey, before my dog. I don't have any bears around here yet, but I started planning for an inevitable bear, bobcat, and Mountain lions by getting my livestock guardian dog. He's an Anatolian Shepherd × Great Pyrenees × Maremma cross that I got from a farm using the parents to watch poultry and goats (exactly what I wanted!) My dog (just turned 1yr) has been watching over my animals since Day 1. He's been socialized properly with my animals, humans, and other dogs, as he does get a break during the middle of the day, when I walk other people's dogs.(which is not necessary) When just 6 months old, he was very wary of new dogs at the park we walk at. And, now, if a dog pushes him, he doesn't back down anymore. He knows "our pack" of about 20 dogs, and his place in it. You can find some pups at a lower cost, if you look and ask around. He's now 120 lbs (lean weight, not fat)
They DO need a consistent, strong leader who doesn't use force to try to get a dog into submission or anyone who hits a dog (they shouldn't own a dog in my opinion) as these dogs ONLY work and respond well with positive reinforcement and interactions. They will respond negatively to force, and they do NOT forget!
But, they will respect you as a leader, if you are consistent with training. Do some research on breeds. My dog has saved me thousands of dollars, keeping predators away from my poultry and goats! He has a very good temperament and loves my family. He's at the age where strangers are going to have to be escorted in my property.
***Also, I know that some people can't have a dog, so HEAVY reinforcement is necessary for any area that poultry are kept in!
You can use metal/over pipes with a flat, smooth piece of wood, etc on the end to keep the bird net, so it is high enough for you to walk in. They have some reasonable bird net, and I don't mean the cheap, easy to rip netting that you would use over berry bushes.
Your coop needs these criteria: protection from elements and drafts (yet having ventilation is important!) Roosts (a step style works well in a coop, and will hold many birds. Try using different width dowels (.5" for younger birds/bantams, then offer 1", 2" etc) round, smooth wood that's not slippery, held onto a frame, or use shower rod holders, etc to hold up dowels! A varied thickness works well in exercising feet during those COLD Winter days, if/when you can't let them outside), and laying boxes. Square footage is important too- crowded chickens fight and are not happy. But, a cozy area during the Winter helps too- a temporary box around the roosts will keep birds warmer.
Place your water and feed up off the ground at a varied height for different ages/size of birds to keep bedding and excrement out of it! I also have a "sandbox " for my birds, using Diatomaceous Earth to keep any external parasites away. It also is rich in calcium, so if they eat it, it's safe for everyone to eat! (People, dogs, everything)
A wooden coop, shingled, with the use of a clear plastic roofing piece, or window & screen used on the sides for light entry is good too! Your imagination is your limitation! Chickens are so much fun to have, and they have individual personalities, so happy chicken stewardship!!
