Albert Barnes on Luke 12:18

I will pull down my barns. The word barns, here, properly means, granaries, or places exclusively designed to put wheat, barley, &c. They were commonly made, by the ancients, underground, where grain could be kept a long time more safe from thieves and from vermin. If it be asked why he did not let the old ones remain and build new ones, it may be answered that it would be easier to enlarge those already excavated in the earth than to dig new ones.

(q) "this will I do" Jas 4:15,16