Like everything else in life, one needs to learn how to use a greenhouse.
Clearly the people who were going to build a greenhouse in the dense shade of evergreens weren't even competent gardeners in the first place. A greenhouse is an advanced gardening structure, and people should be competent gardeners before undertaking the additional complexity of growing under a permanent, weather-altering structure.
I'm loving the *@#$& outta my 20'x24' hoophouse. I was an experienced gardener to begin with (and I put it in a sunny location!) but it's still a learning experience....
How to deal with burrowing varmints (shrews, mice, voles)
dealing with insects--aphids, cabbage "worms", cutworms, cucumber beetles...
dealing with heat in summer (venting ain't enough in Nebraska). I bought shade netting late last year to try out this summer.
managing the soil for maximum production
VERTICAL GROWING!!! (just installed aircraft cable runs midsummer)--it's a revolutionary improvement!!!
how to space your growing beds, when to plant, how to water, etc....
I'm deliriously happy with my hoophouse. I don't think I'd ever want a glass greenhouse--they present additional burdens like building permits (and the additional real estate tax) in most areas, and though double-paned glass can be an adequate insulator, the effect of the sash DECIMATES insulation values. Why pay the additional costs then?
No, it's a hoophouse for me, now and forever. I want nothing more.
It's only my third winter with the house (the first winter was largely lost since the house got installed the last possible moment before snow flew). So that winter it just overwintered some kale, parsley, and perennial cutting starts. Plus, I had to compost away all the tough turf grass that was under the hoophouse.
First summer was spent largely dealing with the tough turf grasses and green manuring. The tough grasses were layered over with corrugated cardboard and mulch. Areas that were soft enough to be turned (not many in the clay soil) were succession-planted with buckwheat to break up the tough clay. A few monster tomato plants also grew there and produced bountiful harvests.
By fall some areas could be planted for a few overwintering crops--onion family, Egyptian walking onion, more perennial holdovers, kale, parsley, etc.
Last year the soil was finally ready for large-scale planting. Basil, lettuce, kale, kohlrabi, spinach, turnip greens, peas, cucumbers, gobs of tomatoes, green beans, and very happy pepper plants. We are still harvesting carrots, daikon radish, parsley, green onion, and kale. Next winter we'll add more root crops and spinach (this year we had too many tomatoe vines to plant the winter crops).
It's all an intense learning experience.
Oh, and I live in zone 5b, Nebraska. It's a sunny 20 degree day outside, and in the hoophouse the temps are in the 50s. (On an overcast day, there is not quite the same heat gain of course!)