sorry folks - I didn't manage to get a sketch of the cold frame from my father-in-law...
here is a better picture of the cold frame - we can lift the cover from either side, when necessary, for ventilation -
the cold frame plactic looks 'foggy', but this is supposed to be good - it diffuses the light in all directions, which should be good for the plants, and also this particular plastic is anti-condensate and has 4 years warranty. I am very hopeful it'll last!
When it'll warm up (late April/early May), I am planning to lift the cold frame from the lettuce/cabbage bed and move it to another bed where I'll be growing melons. And in the fall I'll move it back to the lettuce bed - I am hoping I can get the lettuce survive through the winter this way...