Well (generally) your bf will get more for his money buying a pre-built PC.
However it's definitely a whole lot more fun building your own, which is why the majority of us are here.
IF you go down the homebuild route, the Hardware section here is probably the best place to start asking questions. It's an undertaking NOT to be taken lightly & an existing interest in PC's is a good basis for a homebuilder as speccing components won't be a complete mystery.
And in either case, have a budget in mind, and stick to it.