The problem in the that the roof is a part of the unibody and if you cut it, you would really need to re enforce it to make it safe. Here in Calgary, you'd probably be fine with the insurance co', (they rarely look at the vehicle, so you could just not tell them about the roof), but please make it safe for the rest of our sakes. Now, you could get stopped my the cops or the highway inspectors and they might have something to say about it.