First and foremost, a Lean To conservatory should match the house it is attached to. This makes in some cases iron or aluminium the more obvious choice. I have a fancy for wooden conservatories though.
Against common belief a well made wooden conservatory is as durable and long-living as anything. The main factor, like with any wood construction (and really any sort of building), is to avoid a continuous exposure to moisture right from the begin. This means, the base should not have direct contact with cool and wet soil or capillary moisture in brick or concrete fundaments. Rain water should run off immediately. If the wood can always dry out again, any sort of timber will survive decades or even centuries. Of course, certain woods are especially well suited for this kind of purpose - read more about hardwood conservatories.
Still, the most important element is the right conservatory design. I.e. aluminium capping at the vulnerable points along the apex and roof timbers and a raised base which keeps the construction away from snow and splashing rain water can make a wooden conservatory last forever.
