How can I create an irregular multi sided polygon

I am an absolute beginner to Unity so I apologize in advance if my question does not make much sense.

I know how to create basic objects and how to detect collisions. However I need to create and object that’s more than just a cube. What I need is an object that is an irregular multi-sided polygon in 3D. If I create this then do I need to create it as many different cubes and then stack them all on top of each other?

You should be able to use a MeshCollider (use the same mesh), but it really depends on how complex. Sometimes it’s more efficient to approximate with cubes.