I looked into this too just because it's so hard to find premade ones without getting raped on shipping. But I ended up finding some 100w ones on Amazon for $160 with free shipping so went with those. Also found another site after the fact that sells bigger ones and does not charge that much for shipping. So they're out there, just hard to find as when I was searching most of the sites I found always ended up being in the US even if I put Canada in my search query.
While looking into making my own I did come to the conclusion that it would actually end up being almost the same price, maybe even more expensive. So the only real reason to make your own is if you absolutely can't find/get premade ones. Otherwise I'd go with ones you can buy.