This one is more complex. If the company is explicitly paying you to build something to be patented, they should own it. Making it yourself means not acceptin

This one is more complex. If the company is explicitly paying you to build something to be patented, they should own it. Making it yourself means not accepting their paycheck for the work and covering the associated expenses of your own time and filings. Then you own it and can license it to whoever. If there’s some alternative way of doing this that still incentivizes the company to hire you in the first place, it’s probably worth negotiating up front. Patents aren’t very different from any other work for hire scenario in that the people paying for the work will own the result. If you hire someone to renovate your house and make a ton of money selling it, does the contractor deserve a cut? If so, did he charge you less for that cut knowing it was a flip?