My kids are totally into Minecraft, too. So I understand the concern about wanting them to do something "real life." But what's wrong with telling him his screen time is up and he needs to find something to do?
Can he come up with a list of things and refer to it, rather than putting the responsibility on you to entertain him? Legos are a good substitute for building on Minecraft. At that age, in addition to legos, my boys also made 3-d villages out of paper, they would create popcycle stick structures and also just plain make forts around the house. We also have all kinds of building games-- from styrofoam creatures and magnetic pieces to giant cardboard blocks.
I do have the benefit of twins, who can entertain each other, but I rarely helped them with legos or other projects.
My vote is to let him figure it out.
