Scipt User roles and permissions
I recommend you have a look at the procedure sp_dbpermissions by Kenneth Fisher.

I have been using it and it allows you to list all the permissions of a particular user in a database, and gives you all the scripts to copy all those permissions and apply them on a different database.

In case you want to apply them on a different server as well, that is fine too, but don't forget to create the server login first.