Hi Liam,
I will start by saying, the only experience I have is petting them. However, I've got a little with greenhouses. I think it could be a decent
enough temporary shelter, but I would have some concerns.
First is the wind. I built a hoop house,
greenhouse in an area without nearly that high of wind, and it still got blown over. I built a different framed style greenhouse which lasted on a ridge with lots of wind.
In both cases, if you close it up, I think the heat might be an issue. If you leave the ends open so they can come and go, that
should not be a problem.
Lastly, I would suggest adding some sort of barrier around the bottom 3 or 4 feet (based on goat size). Otherwise, they are apt to put holes in the plastic without trying to.
I think it can work, but it won't be quite as simple as a hoop house for
gardening.
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"When the whole world is running towards a cliff, he who is running in the opposite direction appears to have lost his mind." C.S. Lewis