It sounds like you know what you want, so here are just a few pointers to mod building (I'm assuming you want to build a mech mod from your description)
DIY Parts
Check this site out for all of your parts you need. Secondly, you need to find a high quality switch; most mm vapers (myself included) usually replace the magnets in our switches to get the desired button push. Get a good switch and that way he won't have to change it.
Secondly, be sure you use copper or if not copper at least stainless for the inside battery tube. Copper usually allows for the lowest voltage drop imo. Be sure your 510 threads and deck base are solid copper to really push that conductivity. Most mm vapers love those floating pin positive caps. For someone with a large inventory of batteries however, an adjustible pin is the only option. Also, the more surface area his rda/rta makes with the cap, the better the vaping experience.
Thirdly, be sure that the mod is clean in apperance. When I made mine, I rushed it. Needless to say I spent more time fixing mine after I was 'done' constructing it than I did when I built it.
In conclusion, I think the idea is spectacular! If he's a ResEv fan he will definitely enjoy showing it off; not to mention he can say you made it!! If I find time I'll post a pic of my R2-D2 26650 I made last year. Best of luck, and hope this helps!!