This has always been one of those, “why the fuck don’t we do this already?” things.

Because the black roof lobby has spent a ton of money to keep roofs black.

Not kidding.

"It isn't cheap" seems to be the biggest issue. Saw another video that showed it working, but he did say it was pretty expensive for paint.

This is the video i was looking for!

I don't get why we don't do it either. I live in a dark brown brick oven... the sun literally hits the entire house because neighbors didn't want a tree in their yard so they cut all the big ones down... even when outside it cools down, my house stays hot. Even when i leave all the windows open, as soon as i close them, it warms back up. The house itself just stays hot for a very very long time...

https://en.m.wikipedia.org/wiki/Windcatcher

Grass roofs have been around for ages, but they require a lot of structural planning to deal with weight, water, and when they inevitably have to be replaced, they are more of a hassle. Whereas paint probably just needs to be repainted, or reflective metal roofs last longer while not being too hard to fix (need a radiant barrier, but still easier to work on).

Yes! What you're describing is basically a ventilated roof system (somtimes called a "cold roof") and it's super effective - the air gap creates thermal break that can reduce heat transfer by up to 45% compared to direct-contact roofing.

A shade structure? Yes, a shade structure will dramatically reduce load on the AC of whatever is under it.

Would that help the larger city climate? Well sure, if it's trees. A giant umbrella over the top of a skyscraper? Who knows

That's called an attic. And yes, attics do help the floors below get less warm.

When you have an attic, you can go further by insulating the roof - this keeps the warm day air out, and during the night you can open windows to let the cool night air in. Historically roof insulation was done with thick layers of thatch, though light-weight synthetic alternatives are more common in modern construction. A well-insulated roof won't let through any appreciable amount of heat.

Then as things get hotter, build the roof taller, allow for natural air flow to dissipate the heat, and finally put the building on stilts so air can flow under it.

Retrofitting existing buildings to have space for good insulation is expensive, especially with the atrocities the US has been building in suburbs for the past 80 years.

Loose dark clothing encourages airflow. Covering up prevents sunburn and direct solar heating.

For buildings, airflow can cool them too. But it doesn't need to be done through dark roofs or dark exterior walls. And buildings could have more sunshades and awnings, and smaller windows to prevent solar heat gain.