A traditional approach is to have a timber conservatory which can be painted or stained to any colour you wish.
Timber may be the preferred choice if you require a unique design, or for example, if you have a listed building.
Hardwood is good for an authentic-looking traditional design.
Almost any traditional design or feature can be recreated with it. You also get the benefit of double-glazing. This is the best material for listed buildings. While it will require some periodic maintenance, modern paint finishes and stains ensure that this is increasingly less of an issue.
It's available in a variety of stains (e.g. mahogany, light oak), as well as various painted finishes (white, cream, green and brown).
Hardwood refers to wood obtained from deciduous trees. The word 'hardwood' defines a range of timbers. It has little to do with the density of the wood. Deciduous trees range from Balsa wood to English oak!
Timber structures which have been properly treated can last a lifetime. During the post war years shortages led to unpreserved sapwood being used. Durability problems are now a thing of the past.
This is the most expensive choice of material, but it will look the best.