I was addressing Joe, since the idea of "scattered components" makes me think he's talking about a toaster in this house, a microwave in the house down the street...
However, I'd like to think that it's possible to order the right components and put it together yourself. You could either order a gaming PC from Alienware... or you order the case, the motherboard, the video card(s)... and you build it yourself on your kitchen table. Usually ends up being cheaper that way too.
So I could imagine making a Deck at home, with the right parts and tools. However, all those parts are going to be Restricted, since the final product is Restricted. You can't just use an ordinary processor salvaged from a high end Commlink, it has to be a very specific grade processor that can handle the level of computing a Deck is for. Stuff like that.
Basically, I don't think it's as simple using the Mod rules to ramp up a random device and make it into a legitimate Deck. But it "should" be doable, in theory. Of course, I'm pretty sure earlier editions actually gave prices and mechanics for such a thing. Here in SR5, the company line for Matrix stuff is "no one knows how it works, it just does."