There is a video tutorial on this for third person but i dont remember who made it. But it is simple really; you just set the location of the camera with every Pressed input of mouse wheel up and down by adding/subtracting values to the Z axis. Or you can set the FOV instead of setting its location.
Here:
And dont forget to clamp the values like i did to any value you like so that you dont get crazy FOV as you wheel up.