It should be based on bedrooms.
A four bedroom house should have a minimum three people living there as their principle place of residence. The address on their drivers license, electoral roll, school encirclement, etc. If you have less people, you should pay... I dunno, $40k per year in tax?
The government can use that $40k per house in tax revenue to buy all the homes people are suddenly going to want to sell, and put them on the rental market. In some parts of Europe half of all rentals are owned by the government. It's a system that works well. It also makes town planning easier - often homes need to be demolished in order to build infrastructure for example. The government can do that if it owns a suitable residence with a lease that's ending soon.