Steel and aluminium cold frames are frequently cheaper than their wooden counterparts. They are normally glazed all the way to the ground, which helps increase the amount of light available to the seedlings. However they are not as good as wooden cold frames at storing heat overnight, limiting their use at the start and end of the growing season.
The use of aluminium allows cold frames to be made in designs that wouldn’t be practical with wood; it also has the benefit of being lightweight and almost maintenance free.
An aluminium cold frame provides a good entry point to discover the benefits of cold frame gardening.