[Question] What's a valid Greenhouse?

[Mc-muffin]

Hello, sorry for not following the template but I don't think this counts as a mod issue.

The question is what's on the title, what's a valid Greenhouse? Using the wheater monitor in a couple of self-made structures always show the message about condition being too unstable, so I humbly ask for support on what's a suitable structure that the weather monitor would consider a valid Greenhouse. Thanks in advance