Informational Guide on the Duskwork's Building Sizes.
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.
Note that there are only Gen 1 and Gen 2 versions of buildings for the Core Buildings
Example for Solar Panels:
Gen 3 Buildings for the Core Buildings and Gen 2 Buildings for the Non-Core 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.