I chose this RAM as it has a cas of 8 and is good value, If you are not looking for OC'ing at all then you can go with a cheaper MOBO (possibly get a r9 280 then) but this one should give you a mid OC.
EDIT: Seth's build above is also very nice if you want to go AMD. Whether or not the one I made is more suitable than his depends on what games your son likes to play.