The materials would normally go under nominal 5000 - general purchases. You can of course create your own nominals for specific types of purchases but 5000 will do fine. this is entered as a purchase invoice.
When the item is resold, or repackaged with other items and sold as a complete service you can enter this separately on a sales invoice, by default it will go under 4000 - general sales. But again you can create your own sales codes and change them by clicking on the grey question mark in the sales entry form.