If at all possible position the glasshouse with one end to the rising sun, and the other towards the setting sun, in this way you ensure a constant supply of light throughout the day. As the sun's path varies between summer and winter, choose a happy medium. With this in mind don't site it close to trees or overhanging shrubs which will cast shade at some point in the day. If your site is exposed, try to position by a wind-filtering hedge and accept that some loss of light will occur. You must have a solid foundation for your glasshouse, level in all directions, with the frame firmly bolted to a base.
Most greenhouses come with pre-formed bases so it is really simply.
So there you have it - a few greenhouse basics, and a purchase you won't regret especially at this time of year. It may be snowing outside, but inside your micro-climate of warmth you can tend your plants for hours without worry or discomfort. Second hand greenhouses are very cheap but you usually have to do the dismantling. Rebuilding a dismantled greenhouse is very difficult - and there is usually a loss of rigidity and structural integrity. Aluminium greenhouses are more easily maintained than wooden framed varieties.