VA Retail Sales and Use Tax for Aircraft
I live in Virginia and spoke with an agent in the Virginia Department of Taxation when I started my RV-7 project. Virginia charges a 2% "Sales and Use Tax" on the initial purchase price of aircraft.
The agent told me that, for a "compoment built aircraft", the 2% tax would be assessed against the total purchase price of the component parts used in construciton. However, the tax isn't due until the aircraft is airworthy.
During the build, you should save your receipts. After the airworthiness and registration have been issued, you will need to fill out FORM AST-3, Virginia Aircraft Sales and Use Tax Return. (I think you will need to supply copies of the receipts with the form). And write a check.
The receipts should cover all of the big pieces.