Rebuilding costs for listed thatch

[mrsmastiffs]

Hi, can anyone tell me how to go about calculating rebuilding costs for insuance purposes on a grade 2 listed timber framed thatched property. I am a Loss Adjuster by profession and have all the info I require to do this for a standard construction property but cannot seem to find out any info re: this. The property is approx 900 sq.feet.

Also, are their any specialist insurers that come highly recommended.

Thanks.