Asking a carpenter about painting a house is akin to asking a programmer about the shrink wrap for the final software package.

It is not a good analogy.

Maybe asking him about what sort of wood he has worked with, the sort of things he has built, what stuff he has done in the past.

And a carpenter's job isn't going to take years with weeks of learning the lay of the land, so you aren't so worried about him walking away.