Killington's got it right. On NA_1, sapper constructions are to be used for defensive purposes, that is, on the ground, and not to access areas that are not accessible normally. A good rule of thumb to follow is this: If you can't get to it on foot, don't use BPs to get to it.
What it comes down to is that if someone is allowed to get to inaccessible areas, then they can delay all day, and that's no fun.
Also, it should go without saying that going outside of the map is against the rules. You're lucky I only kicked/temped you guys.