What happens when I sell them?
It matters not.
If it's being sold for FINAL retail sale and never been taxed, it's taxed. Got it?
It doesn't mastter how much it cost you to build it, just how much it is sold to the final retail customer for. Business to business transx are not taxed.
Try harder.
I admire your abilities. I have not built much more than a small shed myself. No doubt the sales of your house and plane would be tracked by the tax authorities and you would be prosecuted if you failed to remit the taxes. The NRST proponents see this as a lesser evil than employers witholding income tax. I'm not so sure. What if you sold 3 planes built from 3 kits but reported sales of two? How would compliance be enforced without lots of material tracking, or spying on builders like yourself, or purchasers reporting their purchases?
I built a $80,000 airplane from a $16,000 kit, and a $250,000 house from $100,000 of materials.
You forget the tax paid on the matterials & kits you use. Once the tax is paid, that's the end of it. What you do with the materials you purchased and paid the tax on is your affair.
If you are an individual (non-business) building such things you pay the taxes on the materials you use to construct your goodies. Pay the tax once but only once is the rule.
What happens when I sell them?
If you are a business doing this for business purpose, you didn't pay tax on the materials you will be required to collect the tax from your customer providing a reciept, then remit such to the state tax authority.
If you are an individual doing such on an infrequent basis. You have paid tax on the materials, kits, etc. And that is the end of it.