Rod Speed wrote:

The way I have solved that kind of problem is by giving the guy a
shopping list. "Any questions? Call me when all the stuff is at
your house and I'll be over"

Trouble is that plenty arent capable of using the list properly.

And its often a lot more trouble to make up a list that someone who
doesnt know anything about renovations can use than to get the stuff
yourself.

So tell the "friend" you need his help to pick up the materials, and remind
him to bring enough money to pay for them. If he for some reason can't do
that let him know you'll be happy to help him whenever the money is
available.