To put it simply, building is not even part of the game. You can place single blocks, or predetermined "clumps" of blocks, but they aren't effective for anything more than helping you get up a few blocks higher when trying to climb something.
Rounds are too short, maps are too small and destruction is too easy for building to be effective. Given that knocking out the bottom row of anything will lead to its collapse and even team mates will bring your structures down.
Mostly the maps have prebuilt worlds with different themes, and its more about how you use them, or destroy them, to your advantage.
Still fun, but very disappointing on the building side.