Push Comes to Shove is the twentieth mission in WorldBuilder.
Using your Bulldozer, clear a path to the goal by pushing the boulders out of the way. Be careful about where you push them, though, and stop by the Gas Station if necessary.
Grab the plans for the Frog located near the Bonus Goal. Using your Bulldozer, start pushing the scattered green bricks together, refueling at the Gas Station whenever necessary; once all of the bricks have been assorted, take apart the Bulldozer and build a Frog.
Alternatively, you can ignore the scattered bricks entirely, drive your Bulldozer near the Gas Station, take them both apart, then use their parts to build a Frog for the goal.