This, via Marco and Waxy, is a little depressing. The proper rules are very different from the way I played.
1. If a player decides not to buy a property, it immediately goes up for auction by the bank and is sold to the highest bidder. This blew my mind.
2. Houses must be built, and sold, evenly across a color-group. For example, you can’t build three houses on Park Place without having two houses on Boardwalk first.
3. It’s the property owner’s responsibility to ask for rent. If you forget to ask for rent before the end of the next player’s turn, you’re out of luck.
4. Rent is doubled on properties without houses in a monopoly.
5. Income tax is calculated from your total net worth, including all properties and buildings, not just your cash. And you have to decide whether to pay 10% or $200 before you add it up.