Here are three approaches to developing content for an online course platform such as Udemy. 

I describe techniques I have used including:

Creating an online course around a topic in which you have a high level of expertise and passion.

Invite a content expert(s) to join you in developing a course. This person could also serve in an on-camera role for course videos.

Journal your experience in learning a subject, and then create course content from your notes and experiences.

These techniques are ones I've used in courses I've created at the university as well as in my courses on Udemy and other platforms.

http://www.udemy.com/u/vickiemaris

https://vickiemaris.com