you might want to take a look at the wiki for building production ratios. although that would be an amazing building, to have a 4:1 production ratio AND a planet buffing bonus would be too much. right now the best building in the game is the assimilation locus (4:1 ratio), and it is one of the hardest to obtain in the game. most buildings obtained through missions have a 2:1 ratio, and most advanced npc buildings have a 1:1 or a 2:1 with some sort of high planet defense bonus, like the stryll interrogation stronghold, with a size 1 research 2, defense 300.

if i may make a suggestion, make it a size 1, artifact 1, research 1, pop 50, and then have the pop double if built under specific conditions on a planet.