The golden bricks are bricks you will not have to build if you restart the tower. 48 golden bricks=you will not have to build 1 floor.
If you restart the tower you will also get boosts (click power, market prizes and production)
They can be obtained by restarting your tower from zero. (if you have already got 48 golden bricks or more then u will not have to restart from stage 0)
You can also get golden bricks from a daily gift.