Our cold frames.

Whether you are starting seeds in flats or sowing them directly into the soil, a portable cold frame provides the opportunity to get your plants going a few weeks early. To get the most out of a garden, you can extend the growing season by sheltering saplings from cold weather both in early spring and during the fall.

Here in Pakistan to produce winter vegetables in summer by creating an artificial environment is much costly so not practiced at high level . But production of summer vegetables in winter by providing them optimum environment in tunnels, as the plastic sheets saves the energy of sun and does not allow them to go back and provides enough warmth for vegetable production.
Here our only cold frames are very cheap low plastic hoop tunnels made from bendable sticks from trees covered with plastic.
We never build or buy sophisticated cold frames or hot beds.In fact never seen one in market.
Plastic costs less than glass and being used for a season but it serves the purpose.
Normally the crops grown are cucumber, tomatoes, summer squashes, pepper and sweat pepper in such tunnel in winter to give early start in spring.

"As you simplify your life, the laws of the universe will be simpler,solitude will be not solitude, poverty will not be not poverty nor weakness weakness."Henry Divid Thoreau Quote".