What does your son do or what philosophy, life viewpoint does he have and what are his favourite colours?
I have one son who is a lawyer and there are several nice patterns suggesting that profession - barrister's block which is quite nice and 2 or 3 others. I'd try to work two squares together and try for a secondary pattern if I could design it. Not sure of his colour preferences right now - he is 42, but would make it with his hair colour (dark blond-y red now, was strawberry blond as a baby and little boy), eye (blue-grey) and lip (sort of maroon-y rose) colours and work a few other contrasts and complimentaries into it. He is single at the moment, but I'd want it to be in colours a new wife would also enjoy.
My younger son is cabinet maker by training and artist/designer of interior airbus structures. There are two blocks, carpenter's square, and carpenter's circle I might combine the two somehow hoping again for some secondary patterns. He has a stated preference for muted neutral colours in clothing which would make for a terrible dull quilt, so I'd look for some rich contrasting neutral and add a dashes of rainbow colours. He is married with three great kids so I'd hope it could appeal to all of them. I might be fun to make smaller less complex versions of either one block or another to symbolize 'chips off the old block' just for a lark.
This is truly dreaming in technicolour as my time is so taken up with work I haven't done one stitch for a month! and have so many ufos it would be immoral or insane or both to start anything else before finishing at least half of them!!!!