Comprehensive cover isn't cut and dry for kit and replica vehicles; getting the right coverage for the vehicle you have built is usually a more much bespoke affair.
Your basic level of cover will insure against everything that a conventional insurance policy would - theft, fire, accidental damage and third party damage.
But your kit car policy can also include various specialised optional extras such as build-up cover, which will insure the parts of your car during the construction process. This can be invaluable given that the sky really is the limit when it comes to the cost of parts for your home built vehicle.
Given that you will have devoted plenty of time and effort to building up your car from scratch, you're likely to already have the expertise necessary to make any repairs. In this case, you can opt for parts only insurance, meaning that in the event of an accident, the insurance company will provide you with the spare parts you need, leaving you to put them together.
Past this, it is possible to get many of the same add-ons as with a standard car insurance policy. Despite needing specialist cover for a kit built vehicle, it is possible to get things like breakdown cover or courtesy car cover if you find the right provider!
It is important to note that many insurers will not offer kit car policy to drivers under the age of 21, given the added risk involved, and if they do choose to insure you, you can expect to pay significantly more than an older driver.