This is a bigger project. You have seen parabolic microphones on the sidelines at football games. They can be any size, so a participant doing this might want to go big. But don't go so big that you never finish it. You can't use it (illegal) to overhear conversation from people who don't know what is going on.
We have some $3 electret condenser microphone capsules that need a few parts to make them usable, then you add some amplification to get up to headphone strength. It has to be battery powered so it is useful outside.
The bigger job is researching what the shape of a parabola is. You make it from squares and triangles of some stiff material, maybe Masonite (tempered hardboard). The real trick is finding the focal point, where you put the microphone. Maybe you glue a little craft mirror in the middle of each square or triangle and visually adjust the angles to get lined up.
Since there is a lot of non-electronic building, this project is a good one to involve a craft-oriented friend in.
The problem with this type of project is that it ends up bulky and with limited use. But if it works, it is really impressive.