I use the numpad for building, in other games like besiege or gmod having a numpad is a good thing since you don't want to bind keys you actually use.
I can live without it though, its just a nice thing to have really, also one of the other reasons I use the numpad is because I like to move bricks with my right hand, and since the numpad is close to my mouse, its kind of self explanatory.
Though I do hear of people that user their left hand to build using laptop controls, they do it so they can still move their view around.