Lean-to greenhouses are next to the rectangular ones in the popularity stakes. They can be attached to a house wall, high garden wall, or over a door. They are almost as satisfactory as the free-standing ones and much warmer. Sometimes plants can be drawn towards the light and away from the solid walls so the plants should be turned regularly. They are slightly cheaper as you only have to purchase three sides. A modification of this is the mini-lean-to which is only as wide as the 2 ft (600 mm) staging it can accommodate. It is invaluable for very small areas, but heating and ventilation can be a problem.
Dutch-light greenhouses have sides of large glass panels which slope outwards. They are very light and make good cropping units but it is expensive to replace the large panes should one be accidentally broken.
Three-quarter span greenhouses have an asymmetrical roof span which means that one side wall is much shorter than the other. This can have its uses in specific cases but they are hard to come by.
Circular greenhouses are really comprised of many narrow side and roof panels arranged to give a rounded shape. They are quite decorative in appearance but the working space is very limited. They are also much more expensive than the equivalent growing area of a rectangular glasshouse.
Mansard-roofed greenhouses have two sloping roof surfaces at each side. They are very attractive but expensive and not really practical as a small unit.
Domed glasshouses are really more of a novelty than anything else, with their space-age shape, although a large one can make good cover for a small swimming pool, and they can look quite nice as free-standing conservatories.
Tunnel houses comprise a series of metal hoops supporting heavy-duty, clear polythene. They are an economical alternative to glass for a large area, but the polythene has to be renewed frequently.
In addition to the basic shapes, there are also other factors to take into consideration.
Curved eaves are attractive, especially if the construction is attached to your main property, but expensive, and by no means essential.
Glass to ground greenhouses have all sides fully glazed. They admit most light but require most heating as the heat loss is greater. The useful growing area is bigger because there are no solid panels to obscure the light.