My father, age 79, wants to build his own AR-15. He certainly has the mechanical aptitude and the time. But what he lacks is the knowledge. He has found downloadable, printable illustrated guides for assembling lowers in the Internet, but not uppers. There are a number of online guides (including here), but he can't really use his phone for that. Can anyone point to one?  Alternately if a good one doesn't really exist electronically can someone point to a good printed reference I can buy for him?

I'd get a copy of the 23&P for starters.

Most handguards will come with instructions.
Depending on which one he gets he might need a proprietary wrench for that barrel nut.
Here's a couple guides for him.
https://wesleyhurd.com/wp-content/uploads/2022/06/Ar-15-Build-Guide.pdf
https://gununiversity.com/how-to-build-ar-15-upper-assembly/
I would suggest he look up some tips and tricks on youtube if he has the time.
One thing you should tell him to get if he's going to assemble a lower would be a 1/4" universal clevis pin for the front pivot pin install.
It makes it way easier!
Or a book: Assembly book

There's still a million on Youtube.   Bring your phone...stream it to the TV.  He'll laugh his ass off. My Gdad did.

You can download this link as a PDF or at least with Brave browser you can.  Not sure about about other browsers



https://www.ar15.com/forums/ar-15/Assemble-your-own-LOWER-UPPER-FREE-FLOAT-TRIGGER-GAS-BLOCK-Step-by-step-instructions-/4-226782/