You can use your own builder, but it may be better to use a builder approved by your insurance company. You insurer can give you a list of approved builders.
If you decide to use your own builder, your insurer will usually ask you to get estimates from two or three different builders to get a proper understanding of the work that is needed and how much it is going to cost.
Using an approved builder makes it easier to deal with any problems that arise as a result of repair works. If you experience any problems or have any complaints contact your insurer straight away.