Looking for suggestions on different user roles best design practices

I am going to have about 3 or 4 different access levels and some content should be available to some users and some not. I am looking for some advice on how best to do this.

For example, I thought of when a user logs in, they are presented with different navigation panels depending on their level of access. So, there could be a switch statement which would then include different navs like:

nav-management.php
nav-operator.php
nav-admin.php

etc.

Or, is it common practice to show one navigation for all users but when a user clicks on a certain item a check is done on their access level and if not authorised, a message can popup stating they they aren't authorized to access that.

I have a similar question around the dashboard. I could use the switch statement again and display different dashboards depending on the access level of the user or code each widget on the dashboard to only display for certain access levels.

I am not sure if there is a right or wrong way of doing this but any advice would be appreciated.