First, I got inspired by old retro cameras which I wanted to base my design. I used 3D studio MAX to design my camera but you can use whatever you feel most comfortable with. Here are some 3D renderings of my design.
I won't go into detail on what a pinhole camera is but in essence, it is a simple camera with no lens but a small aperture (made with a pin) that projects an inverted image into the film. There are many factors to consider for the pinhole specially the diameter of the hole, the distance to the film and the type of film you are going to use. I found a website called MrPinhole
that summarizes the most important features.