Rome is a snowboard company started by the guys who designed the custom - loads of my mates have them and love them - and they're much cheaper than Burtons.
Anyways, what the guy at the shop will ask you is:
- How tall is he and how much roughly does he weigh? (this will dictate roughly how long the board needs to be)
- How experienced is he? What sort of riding does he like to do? (this will dictate how 'stiff' the board has to be, the stiffer boards are for more experienced riders who like the piste and the park, more flexy boards are to soak up the bumps off-piste or for internediate riders
My advice would be to get him a voucher for a snowboard rather than buying it for him, as what you ride is a really personal choice.