For ours, which is some kind of hard plastic siding:
Some siding cracked, needed replacement.
The wax automatic window openers need inspection/maintenance and we've already replaced several.
Even with the automatic vents, it gets too hot in the summer, so we have thermostat controlled exhaust fans
Winter, we have to watch the weather, if it dips below 28 then auxiliary heat is needed.
We're currently using one electric oil heater, but we lose plants sometimes, we really need two.
Plants in the greenhouse generally need more water.
The heat and fans mean higher electric bills, plus we use heat mats to start seeds. The need to water more often means higher water bills.
I still love the greenhouse but I avoid starting it up unless it is needed.