If you "wait" for other people to do things for you, you'll never get what you want.
Ask him to take you to the store to buy the materails, and ask him for his advice on how to build your table top.
Seriously, take control and possession of the project. By asking him to help you will only help your chances. Reallyl, it'll make his month to be able to do a project with his son.
(I wished someone had given me this advice when I was a teenager)
L8R
__________________
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger