snifflumpus
Planning/zoning will kill you, it's simply illegal to build most types of houses in most of the US. There was a recent blog post about this I can't find, but it outlined all the houses that exist that are now practically illegal. For example, mixed use where there's a business on the ground floor. Or building 3 stories in a 2-story zone. Or having an ADU. The list is endless. In fact my current town just made it illegal to build single family units next to multi-family (with a buffer), and we only have two places in the town where you're allowed to build office space. Retail is slightly better, there are three places that's okay.
If you get through planning, then permits will kill you. The permits to demolish our place (different town!) were more than buying a new house. I'm not kidding.
If you get through permits then good luck with inspections.
What musk is doing with tunnels is what the entire tech industry is doing: working in a zone with a lot less rules. It's illegal to make a building but you can make any website you want. Though that is going away too, it'll get regulated to death eventually and you can already see it starting to happen with data and privacy laws.
The main escape from all this, as far as I've been able to find, is Texas. It's apparently still legal to build things there.