I have always wondered what exactly constitutes being refused insurance. In this case if the insurer has not actually issued a letter declining to quote, has the OP been refused Insurance.
What would he have to tell an new insurer, perhaps," I asked XXX for a quote but they dont do polycarbonate roofs" would be adequate.
That could come perilously close to a misrepresentation if it is not factually correct.
OP has not indicated
why the insurers actually refused cover over the polycarbonate roof.
The answer to that could determine how best to answer the question.
The OP says that the roof is present for 17 years. How long has the house been insured with the current insurer with this roof in place ? Did OP declare the roof to the insurers in question ? If not, there may have been non-disclosure or misrepresentation under the general heading of non-standard construction as it relates to the materials of which the property is constructed. In the latter event the policy could have been voided at any time.
In the alternative, if the OP did declare the roof to the present insurers and they granted cover the underwriters' position becomes contradictory. It is also possible for insurers to change their underwriting criteria by times and that can become a bit of a problem
My suspicion is that the OP may be the victim of tick box thinking (or non thinking to be exact). I had an experience a few years ago in getting a quote for household insurance over the telephone. There was one small element of non-standard construction in terms of material in the structure. Because that did not conform with the binary "yes" or "no" checklist a quote was refused on the grounds that the risk did not conform to their risk profile or underwriting criteria or whatever.
Subsequently, I complained to the company. Surprisingly, they were one of the bigger and reputable household insurers. On examining my complaint management accepted that the non-standard material was actually a risk that they
would underwrite without loading or difficulty and they formally withdrew their refusal to quote. This all happened because the service agent was a de facto robot enslaved to the computer and who had no authority to exercise proper underwriting judgment.
Getting back to cremeegg's question about refusal I always take the view that anything that could be remotely construed as a refusal must be declared as a material fact. IMHO it is just too risky to do otherwise because you leave yourself wide open to being accused of non-disclosure or misrepresentation. Insurance proposals are regarded as legally strict in terms of proper declaration of fact and information. If you declare all the material facts there is no comeback to you in relation to such matters.