how do I respond to this? if i were to make a pigs pen i would use 12/6 boards and do the needed to be able to make a real life sized one and how many i would ect.

You could respond by saying something like, "That sounds like a great plan! Using 12/6 boards for the pig pen is a good idea for durability and size. Have you thought about how many boards you would need and the dimensions for the real-life sized pen?" This response shows interest in the person's idea and prompts them to think further about the logistics of their plan.