One could write a entire book on doors.
I have made two teardrops so far and that was often my question too.
It really depends on first your design, budget, material, and handles you like and lock the way you want. (there are several types) look on e-trailer.com
You may want to buy a pre-made doors Then the manufacturer should have a template of the door for you to cut out of the wood.
Will you be camping in areas that get really cold at night? Are you making a trailer really lite, have thin walls or thick ones.
I use wood, my walls are 1/2 thick with thick isolation, my fist door was made by a friend, my second trailers door I braved it myself with hand made windows too. Called Walley Windows. My first doors were made over night and were just the outside wood and hinges. For windows I had what became called Gun Ports. I cut out a slit and taped a larger pc inside that was taped at the top and covered the hole. and used a padlock on the outside for my lock.
I use commercial door hinges but there too are lots of different hinges and you could make them your self.
When you cut the skin for the outside of the trailer You will be cutting the outside of the door from that same skin.
I start with 2 4x8 plywood clamped together so I have the same Trailer and Door outline on both pc's.
I have camped with several hundred teardrop trailers, over the past 20 years of teadrop camping. Very few are alike when it came to doors.
So when it comes to a door you really need to define the whole trailer design and what you are hoping for as the end result. size big wide, tinny narrow, gull wing or regular, one did a slide. One door, two, back door only.
Look at the Build Journal some offer pictures. Then you need to re ask your question after knowing What you want it to look like isolated or not
Then it depends on how carzy you want to be. One had his 3' high and carried a large boat on top, One made his look like a jet fighter.
So are you going basic or on a little of the wild side. Some teardrops have slide outs, some fold down second story, some offer a bath with shower. Some have port windows, I started with a pre-manufactured window to home design.
So once you know what you want in design, the shape, and thickness then you will know what your door will look like and it's window.
Then you can reword the question. I know what I want for a door and window for my trailer, I kneed help making it.
Ron