The house insurance in this case is a part of a mortgage contract or voluntary insurance? And if it is a part of a mortgage (as an extra payment), how does one predict how much they will have to pay for unexpected things like fixing the roof, and how does one estimate the full cost of a loan?

Also if it is a part of the mortgage why doesn't the lender pay for it? They need it, not the homeowner.

Is insurance company affiliated with companies doing the repairs?