Lets talk about the obvious difference first. price. Although Factory made looks great, It costs a lot more then making your own.
If you have a tight budget, then forget the factory doors. By the time the dust settles, you're looking at around $1000 for 2 doors.
They Make the trailer look professional, have a double lock and an adjustable screen, but they can put your project over the top when it comes to cost.
The whole trailer build is really about doing it yourself, And that might mean making the doors yourself. Whatever you choose, doesn't really matter at the end of the day, because when you're getting tucked in at night with your significant other, all that really matters is that the bugs and rain stays out, and the dry sleeping bags stay in.