This is a game and doesn't work like real life.

Stability is determined by how many building pieces you're away from a piece connected to the ground. The more pieces away the more unstable it becomes until it just falls down if you try to attach it. Blue is the most stable (attached to ground basically) then green, yellow, orange and red.

So in this case if you're attaching your beams to a wall section that is (for example) orange the beams aren't going to all of a sudden give you green support.

There are building materials that will provide ground support for two or more building sections which will allow for larger buildings to be constructed.