Love the comment about kids. Except last year my daughter was helping shovel and the ice was so friggin' slippery she fell and broke her wrist.
Up here in Minnesota you have to get that snow gone quickly. We are in a north facing hangar. If I can get out there after the snowfall but before the plow comes through it is best. I have an old lawn tractor with a blade. I can usually push it all away. When I do this our awesome city guy (hint: get to know them - be nice it helps!) will then not plow me in.
But (being a renter) you can never stop the roof from dripping melting snow right down in front of the hangar and turning into ice. So at this point you need to do the absolute minimum. As others have said, just chip out the 3 tracks and forget the rest. With our bi-fold door we then have problems shutting it! So I actually use a pair of ratchet straps to get the buckles closed. For the sliding door you need a way to quickly cut a groove in it to where it will chip out. Its too bad you can't lay long pieces of plywood on edge (say 2'x8' or 2'x12') right up against the front of your door across the entire span. Then when you arrive pry them up and out and the door should slide freely. Heck you could probably even screw handles onto them.
I know others have advised against salt. Actually our city guy (upon request) came and put down something rather than me getting out salt. It was enough to get the ice out. It was probably salt LOL! But there is the irony. They have build hangars with roofs that barely overhand the door. There is going to be ice. Probably better off in the end using salt when needed and they can consider it a long term expense vs doing the roof right in the first place. I have used one 10lb bag of salt over 3yrs so its not like you need a lot.