I did the double slice pattern for quilts for my DH and my brother at Christmas. I used Trail's End for one and Catch of the Day for the other. Does your grandson have any specific hobbies/interests that would help you decide on fabric? I am currently looking for some duck/geese/hunting fabric for a quilt for one of my sons. I'm having a hard time finding something that I like.
I think a log cabin block is another good one for guys. There are so many variations to choose from.