When considering a wooden greenhouse there are a number of things to consider: Firstly, what kind of wood is it? The best quality wood for a greenhouse is Western Red Cedar from Canada, The grade that we use in the Alton greenhouse (no.2 Clear and better) is relatively knot-free and is an attractive mix of shades from almost white through shades of red to a dark almost mahogany like brown. Other timber greenhouses such as Swallow greenhouses use Thermowood - a heat treated softwood which has very stable properties (ideal for painting) but in its natural state it does have a rather brown appearance and a bonfire-like smell. Some greenhouses are also made from tanalised (or pressure treated) timber, This is fine but remember that pressure treatment doesn¹t seem to be half as effective nowadays since all the potent chemicals were banned from it!
Some models have features which cover the most vulnerable parts of the greenhouse from the weather and removes many of the traditional maintenance jobs from the greenhouse. For example on some of the Alton Evolution models, you can choose optional aluminium bar capping instead of cedar.