Three things decide your premium more than almost anything else: the age of the roof, what the four-point inspection finds, and whether a carrier is writing policies in that area at all.
Roof age
Many carriers will not write, or will surcharge heavily, a roof past a certain age. A great house with an old roof can be effectively unbuyable for a financed buyer until the seller replaces it or credits for it.
The four-point inspection
Roof, electrical, plumbing, and HVAC. Older systems can raise your premium or require repairs before a policy is issued.
Carrier appetite
Some areas are harder to insure than others. I have you get a real quote on a specific address before we go under contract, so the payment you budget is the payment you get.