I have never seen a corded snowblower, and I know that I, personally, would run over the cord immediately. YMMV. I'm guessing that they are aimed at clearing a sidewalk?
I think that if you get enough snow that you need a roof rake, you need a more serious snowblower. Not necessarily a huge, top of the line snowblower, but a gas powered 2 stage mid-price snowblower, at any rate. I bought dh a good snowblower for his birthday about 5 years ago, and it's pretty much his best friend after a couple of bad winters.