Themes are always good. If he had a favorite sport [etc.], you could use that.

well depending on what colors he like you could a metal based room, get him a metal desk (with wood is good), Silver picture frames, a metal shelf, or you can paint the room his color and buy a black schemed dresser or bed set

go with something that suits the parents' needs as well the boys hobbies and interests.
start with the basics. go with a wall color that will still work if his interests change. keep furniture items basic. a bed, a dresser, a tv stand (?), a nightstand. these should be like the paint color, able to be used if the room is redone.
for the "second layer" add in his favorite stuff. themed bedding, curtains with his favorite baseball or football team logo, posters, maybe some model cars or figurines (plastic) from his favorite cartoon.
to make it extra special invite him along to help shop for these things.
third, make sure that he has plenty of organizational space. toyboxes, maybe a shelf with several container to keep his school and art stuff in.
a place to put his backpack.
it's a very cool thing you are doing. i hope he loves it!

you can get some boy's bedroom decorating idears in this site.

We have two boys that share a room. They have different interests which makes it a bit more challenging but here are some suggestions:
1) Washable paint. Boys cannot keep their hands clean.
2) Ability to hang pictures, posters, medals & more. This can be made with a bungee chord, colorful clips, and two well mounted nails or hooks. (We used plant hangers with anchor bolts) They have changed pictures over the years without more holes in the wall.
3) High shelf for sports trophy's or game balls.
4) A place to shove their neat stuff. We have a stack of plastic containers one for cars, cards, neat stuff etc. They can pull one out at a time as their interest changes and they can stack neatly in the closet.

Just a clean room looks like a remodel job for some boys! How nice you are to do this, he is sure never to forget the gesture.

Ummmm… idk just don't put a little kids menu in front of him at iHop because that always makes me feel like everyone is treating me like a child… and i'm not! No, No, No, NO! Rawwwr! >0