If it can be established that the seller faked the report, then you may have a claim under the Misrepresentation Act 1967, you could also look at Property Misdescriptions Act 1991, to see who else you can go after. I suspect your lawyer is trying to establish evidence around the document. Depending on how this came about, you might have a complaint against your solicitor. However, this claim is not straight forward, you have to establish that the report was faked for the purpose of convincing you to proceed, against the backdrop that you didn't have a proper survey. Your claim is unlikely to be worth the value of a repaired roof, more likely the minimum necessary repairs. Probably one for money claim online/ fast track county court.
There is unfortunately an issue, that if this report was not discussed between conveyancers and there is a "whole contract" clause in the contract stating that the buyer confirms they have not relied on any other representations from the seller, then unfortunately the claim will probably fail. As the misrepresentation is excluded.