Comment your opinion: so buildings don't make the earth any heavier because all those materials were already on the planet, right? i was thinking what about trees (bare with me) like when we get seeds from them, what if we just continuted to plant them and never cut them down? i'm sorry if this is dumb lol but what do you think?

Buildings dont make earth heavier but they make that area which it is built upon heavier.

Earth is a closed system as a whole so the energy neither gets inside or out. This is the law (thermodynamics, Google it).

if you keep planting trees, there will more fodder for animals or mankind can cut down for settlement or some natural disaster or they will not get enough sunlight, the trees will be stunted in growth (say 1 tree = 20 plants) in the end it remains equal. It is bound to happen. there's always a reaction.

Don't think in terms of mass but energy! and remember no questions are dumb.