If you are interested in seeing what we have done this year (2008), you can see our homemade greenhouses in action at:
There you'll see our three homemade greenhouses, links to lots of pictures about what we grow and what we have harvested from the greenhouses, and some links to other pages that show a high tunnel and a low tunnel from kits, and a PVC greenhouse that is homemade. They are all great structures and work very well.
For example, we're hauled in 175 pounds of winter squash from just half of one of our greenhouses.
All my greenhouses are homemade. I haven't gone the kit route for several reasons. First, you have to build the kit yourself anyway, and there are plenty of extras to buy to make it complete. Second, I need more strength and woven poly to withstand our strong winds out here. Third, I believe I can build something twice as strong at half the cost when I do everything myself. Fourth, everything is available at the hardware store (except the UV protected poly).
With respect to pollinators for the greenhouse, our experience this year shows that we can hand pollinate with small paint brushes, and then when the bumble bees take over, there isn't anything else that needs to be done. It becomes their greenhouse, not yours.
Lastly, we are venturing into the winter with some cold weather crops. We are growing mostly turnips, Swiss chard and lettuce. The greenhouses should provide sufficient warmth now that we have added row covers to the interior. If you are interested in what you can do in the winter with simple protection, you might want to read my discussion about winter gardening at:
I don't have much experience, but I know that broccoli, Brussels sprouts and kale don't like the heat, and if planted in the spring they'll grow well until summer and then wait until fall before they kick into high gear. With double protection from frost, you might have some of these growing well into the winter, and you'll be harvesting vegetables long after everything else has rotted down to particles on the compost pile.
The idea with winter gardening is that you mostly harvest during the winter, you don't really grow all that much. Surprisingly, this spring our lettuce survived well into the teens and even the single digits, and with triple coverings (greenhouse and two row covers) you can probably harvest about 20 or more varieties of cold hardy crops over the entire winter – all with no added heat.
Gardening isn't just for summer anymore.