Yspahan
In the 2-player game, is building an extra or an action?
Several players describe building as one of the dice actions in the 2-player game, with no designer ruling.
It is an action. In the 2-player game you set aside a group of dice to build instead of taking one of the other actions with them, so building uses one of your actions. The active player can therefore build once for each of their two actions, which means two in one turn.