there is so much...is he going to buy a use tank? does he want glass or acrylic, why? does it want a sump or run an on the back skimmer? If he does want a sump, does he want an overflow box, or does he want an overflow and is that external or internal? and thats just the tank...
I also think every tank should run carbon...
Is he absolutely sure he only wants fish and no coral what so ever, or is there a chance that he may want coral at some point...because if its a possibility, then I would begin to build it with that in mind...
Budget is also a huge determining factor...it will dictate everything...