Gen 1 vs Gen 2 vs Gen 3 Buildings

Informational Guide on the Duskwork's Building Sizes.
The "Generation" specification for building references the quality and age of a Duskworks' building. The first generation buildings were made with incredibly expensive and hard to find components, making it nearly impossible to fabricate without Earth-side resources and accommodations. Generation Two were the next to be created, taking up more space than the previous generation in an effort to make it more cost-effective and easier to produce on Mars. The Generation Two was more successful than the Generation One in creating Mars-buildable buildings but Generation Three is the first generation to be able to be constructed by fabrication-specialized independent settlers, rather than only AADZ.
The only difference between Gen 1 and Gen 2 CORE buildings is the size. Gen 1 buildings take 5 less space than Gen 2 Buildings. To view the exact numbers, check out the player guide page for the building.
This makes the Gen 1 versions of buildings more valuable than Gen 2 versions of buildings.
Example for Solar Panels:
Gen 3 Buildings have a maintenance cost. You'll need to periodically do tasks on them to reduce the hazard level otherwise the building will shut down. You can find the way to do that inside of the building's recipes.