Blast, I remember making a bullroarer out of a ruler as a kid.
I never really thought of them as anything but a toy.
After searching on the internet and finding out more about them it seems like a possibility.
I am going to try making a few different ones to see how loud they can be and how simple they are to make.

It might even be possible to make one into a multiple use item or out of something that would be normal gear. (Hiker's trowel?)

Wish me luck.
The videos I saw make them seem very loud, but I never know if that is really true or not until I do it myself.