How can I make an exterior door?
It is of course possible for an individual to make a door that provides a normal level of performance. The probability that a person without knack for or reasonable experience performing finish carpentry is, however, rather low.

To perform to a normal level, a door needs to fit within a tight tolerance and maintain dimensional stability without twisting or warping. Typically, doors which are not manufactured in a factory are fabricated in a professional carpenter's workshop. It's not really a do it yourselfer's project given the standard to that appears in the photograph.

As an alternative, a used doors from local building recyclers are a reasonable option if a person is patient and diligent. Modifying an existing used door is another option that requires less specialized knowledge.