Aluminum is perhaps the most durable of the two materials, but the wooden-framed glasshouse is definitely better looking, and more sturdy. Of course glass is the most common glazing material, but horticultural grade plastic is an alternative, although perhaps more expensive. Polytunnels are the current vogue, and are the subject of an article next month. Heating Paraffin heaters are perhaps the most widely used, and underrated. With many paraffin heaters specifically designed for the glasshouse, they are cheap to run and relatively clean, although well-trimmed wicks must be maintained to ensure a smokeless burn.
Gas heaters are also available, and are extremely clean to run.
Available with thermostatic controls, some run from the mains supply, whilst others require gas cylinders, they are however more expensive to run than their paraffin equivalents. According to most reference sources, electrical heating is the most reliable and economical, thanks to precise thermostatic control. It is obviously the cleanest form of heating, but I can only imagine it would not be economical when compared to paraffin. You must also consider that power cuts are most likely in winter, and so a paraffin heater in reserve is essential. Other Equipment Ventilation is extremely important, as during summer temperatures can soar unexpectedly and scorch tender plants.