If by "modular home" do you mean what art 550 refers to as a manufactured home, which is what most people around here call a modular home?
If so then all you normally do is run service drop or lateral, metering , and service conductors to the service equipment already installed in the home. The rest of the wiring is already completed at the plant where the home was made. If they will be putting it on a basement then that will need wiring installed on site.
If you mean something that has sections built off site and then assembled on site you really need to find out from the seller what it is that you will need to do as it can vary greatly from one of these type of places to another.