Permanent cold frame?

This year we're using a space down the side of our house for growing almost all our salad as well as Florence Fennel and a few Kohl Rabi we couldn't put anywhere else. Everything seems to be doing very well under wondermesh, even though there isn't a huge amount of direct sunlight.

The space we can use is about 8ft x 3ft, widening to about 4ft. House to the north side, 6ft high fence to the west, open to the east, path and garage wall to the south. The house and garage are rendered and painted, so aren't dark brickwork which possibly helps.

We've thought of turning the area into a semi-permanent cold frame, with plastic for the cooler months and mesh for the warmer ones.

Any ideas as to how we could do it, and reasons why we shouldn't?

Oh, and the ground slopes from west to east, so the damp course is quite high.

We've got an aluminium one that's done very good service, but the polycarbonate is beginning to break up. This year we rigged up a temporary one too, using plastic sheeting, because we needed more space.

We'd thought of trying a winter hotbed, using manure. If we use your idea of a brick base we might be able to do it.

I don't think OH would be happy using old window frames, mainly because there's a heck of a lot of broken glass almost everywhere in the garden and we've both cut ourselves quite a few times just simply pushing something into the ground without gloves on.

Would corrugated plastic give enough insulation, or would the corrugated shape mean it's too draughty?

The twin walled polly carb is strong enough to support it's self but not to support anything on top of it though.

Im building 2 cold frames on the lotty over winter for use next year and will be using the afore mentioned for safety and for it's insulating propertys.