I keep my Temperates (VFT's, Sarrs., Temperate dews) in the greenhouse over winter where they get a climate near to that of their natural home, and also keep some of my highlanders/ultrahighlanders in there also, as there is quite a variation in temps/conditions depending on where things are placed. I have supplemental heating to keep it above freezing in most parts of it, some areas slightly warmer, some colder.
I am not sure what qualifies to some as enough to warrant having a greenhouse, however not living in one of those nice climates where a person gets ideal temps/conditions without a lot of extra effort, thinking or work, we have to do what we can. (I have grown CP's and other plants for MANY years before ever getting a greenhouse, however after growing outdoors, indoors, and in cold frames, a greenhouse was a natural next step. Yet one I would not have known how to take successfully without the experience of the other steps I had gone thru.)
I personally love my greenhouse and with it & a bit of effort, I can give the plants I have that do not appreciate the "local outdoors" a chance to live and thrive. It does take a lot of work at times, but it doesn't have to cost an arm and leg to do things if you think things thru. Indeed keeping a "tropical hot house" type greenhouse would cost more to heat than most plants are worth, but there are alternatives to doing anything as expensive as that. One must only use a little more than a bit of common sense and be willing to put in some real work. They are a big responsibility and can get out of hand very easily, but can also provide an opportunity not ordinarily available.
I would not recommend one to most people, unless the person really needs one and also is truly serious about the hobby long term. It would help greatly to understand the dynamics of a greenhouse BEFORE deciding to buy one (unless you have a lot of money to throw away!). Doing some actual research on them and starting with a cold frame for a year, and then possibly on to a small, inexpensive hobby greenhouse would be the best way to go for most people. (The plastic/polycarbonate & aluminum type I mentioned earlier, like the one Frilleon linked to perhaps.)
Indeed you can create the cold and wet tropics of Mt. Kinabalu, the environment of northern bogs, the wet savannahs of NC, and the wetlands of the southeastern states, (or even a desert if you like cactus instead) all in your own back yard! But it is going to take some real work and understanding. A greenhouse isn't going to do this however. A greenhouse is a tool with its own limitations! But a committed grower, with a greenhouse, some money, knowledge, understanding, common sense and a whole lot of work, CAN!
Greenhouses are NOT for everyone and will not solve all your growing problems just by throwing a bunch of plants in one. In fact you can't find a better, more expensive way to cook or kill your plants! It can easily create more problems than it solves! And if you cannot grow terrific plants without one, you won't grow them with one either. (Most people here do NOT need a greenhouse by any means!)
A greenhouse will rarely help a grower to establish a hobby for many years... But it is often an ideal environment for growers who have a hobby that has been established for many years already.
(And if you don't understand what I am saying, then wait to buy one until you do!)
But if you do some actual reading up and learning about greenhouses, along with learning from a few years of growing experience and rolling with the punches, you will not find a more fun place to play and grow plants!
Just my opinion.
Good luck all!
If you are someone who just started growing CP's and can't wait to get one, it is unlikely you will have long term success with one. As in growing up, growing plants, and gaining wisdom, patience is the key.
Again, just my opinion.