My greenhouse is an oldie. I bought it secondhand in 1984 It's a Halls cedarwood house. Having used parffin heating then propane gas, I realised I was wasting money. I replaced the roof glass with polycarbonate 4mm. Thge structure is boarded to about 2.5feet. Then glass. I prefer wood framed construction. So much easier to add internal fixings. Inside, is lined with small bubble plastic sheeting. The large bubble plasic is usually quoted, however as I am always experimenting in and out of the greenhose. My preference is 'small bubble plastic' This remains attached all year. I normally replace it say after two or three years. I tend to keep plants ticking over, except for lilies, these rest, but are kept watered, just as if they were planted out in the open. I lose very few plants. A danger when winter storing is, too much top growth and lack of ventilation. This will invite mildew and damping off. If you have a structure that is all glass, then you can easily errect a screen of wood or even other protective substance. Cover the lower part of the house outside. Inside, take the bubble plastic to the ground level. No, I don't use any form of heating now, yet believe it or not, I can take cuttings of most plants 24/7. Hope this helps. Please feel free to PM me. Happy gardening. Mike.