Solarpunk buildings should be built to fit their environment – what’s practical, energy efficient, and even what materials are available will depend on where the scene is set. A solarpunk community set in the desert would have to look much different than one in a temperate rainforest, or a prairie.

This is a departure from our current society, with its wealth of fuel and concrete, which tends to drop the same cookie-cutter buildings into every climate and just burn more fuel to heat or cool them rather than adapt the design to its surroundings.

That said, as with all things there are exceptions to every generalization. Solarpunk doesn't generally take a clean slate approach to worldbuilding, and reuse of structures that already exist is almost always going to be more efficient than new construction. The embodied carbon of buildings is estimated to count for 11% of global carbon emissions and 75% of a building's emissions over its entire lifecycle. Or to put it another way: The greenest building is the building that is already built.

https://metropolismag.com/projects/oslo-workplace-reused-materials-mad-arkitekter/

For a more in-depth look at specific materials, see: solarpunk building materials

Light colored rooftops can - though changing this on a mass scale may involve some problems with a well-entrenched lobby bordering on a conspiracy