Like the others I'm not advocating repelling with out proper training. Using paracord as anything but a last resort is rather foolish. But if the choices are roasting like a marshmallow or trying to learn how to fly or levitate while falling. I would risk repelling with 550. Hey, If it breaks you are no worse off than if you had jumped. Maybe better because the fall started at a lower height.

So if you absolutely have no other choice here would be how you would try it.

First double the cord if at all possible. 1100 lb. break strength is better than 550.

Learn knots so that you can tie one that puts the least strain on the rope. You will have to tie at least one to anchor the rope. Along with that you have to figure out an anchoring system ahead of time.

Where the rope goes out the window and over the ledge pad it with something to reduce the risk of the rope being cut. A doubled up jacket or some other clothing can work in an emergency.

A harness is nice. But if you have gone that far you should go the extra distance and have the proper rope and an edge guard. But you can repel with just the rope. There are techniques that you wrap the rope around the body and use the friction as a break. Again these methods can be learned when getting proper instruction.

OK, you have started your decent. Don't use those bounding drops you see the swat guys in the movies use. The stops and the extra shock adds a tremendous amount of strain on the rope. It is called G-Force loading. You are pushing the limits already. Any increase could mean a long drop. What you have do do is slowly methodically walk down the side of the building. Your feet against the building will support some of your weight putting less strain on the rope. Going carefully will lessen the chances of shock loading the rope.

Again I don't recommend this method. But by using these tricks. It should improve your chances. Maybe just enough that it might work.