mm... if he's going for a gaming rig, i'd probably start with a minimum of 500W on the power supply. and a week should be fine.
but to speed this search up:
1) how much space does his place have. there's two main kinds of motherboards he has a choice of, ATX and Micro-ATX. the latter's what you'll find computers under a foot and a half have, while the former's what everything else uses. the main one you'll find most people run are mid-towers, which run between a foot and a half and two feet usually. taht's just how tall they get though, how long varies a lot so there's no real measure to that. but if he's got the room, a mid tower would probably be best. you get enough space to mess around with peacefully but it's not friggin' huge like a full tower can be.
2) how much is he willing to spend. since you're not building it the price probably ain't as cheap as it could be, but a good sale can make most of that off by a couple bucks.
3) how much tinkering with the insides is willing to be done. RAM is cheap nowadays, constantly you'll find 8GB of RAM going for $50. vid cards are notorious for dropping quickly as new tech comes in, and hard drives don't even need to be mentioned with how insane that's been. those are 3 of the easiest parts to switch out in a computer (or in a hard drive's case, put in as the case should have a couple extra slots for more) and require minimal knowledge - you open it up, if you're replacing something you unplug anything connecting to it and take that item out, put the new one in. so long as you're grounded to avoid static electrcity (touch something of similar metal beforehand, even part of the case will help, and stay in contact with it for the easiest way to fix that) you should be fine.
the 3rd one is the one that matters most to price. if you're willing to do a bit of work, then your options open tremendously - as does the price range you're dealing with.
--
The future must protect the clone's past.
"Maybe it's a tentacle, molesting the planet itself. - Aschen Brodel.