I'm looking for an inexpensive way to cover my ugly exterior door.

Everyone has an idea of "ugly" but over the years I have painted our door many times. Since your paint doesn't adhere I might strip all the paint and apply a good metal primer. I have a favorite word that I use all over the house so applied magnetic stick on sheets to letters I had painted using the very same paint and then just place them on the metal Door as the letters are now magnetized. That can work on any shape if you are more creative than I am. Thing about metal doors...they don't wear out and need replacing.

I was also looking for this kind of creative ideas to cover some ugly parts to make beautiful of my office space

http://halsca.com/

Strip[ off the existing paint with Cotristrip a safe non-toxic remover,clean,use a primer for metal,allow to dry and paint the door with a paint for metal.

Remove or sand the peeling paint. Use a good primer then repaint.