What to replace plastic conservatory roof with?

[DecisionTime123]

Looking at buying a house with a brick built conservatory, so brick base to waist height then full upvc double glazed windows and doors on 3 sides; 11' 3 by 5' 6". Has an electric radiator installed. I'm not a fan of conservatories in general but it's in very good condition. The roof is currently made of two sheets of clear corrugated plastic so I am thinking along the old "too hot in summer too cold in winter lines" - what can I do? I can't afford to have a proper roof put on; someone said about a thicker plastic roof or coating the plastic with something to give some insulation?

What's the cheapest way to manage it? Any experiences?

I think insulating with King span internally and then cladding with uPVC would be the best option until you could replace the roof.

Thanks @Stickytreacle - I've just been looking at a system called Cosy Panel which sounds like the same thing. In the pictures it's like white upvc sheets. Might work out ok?