Define `become=yes' per role with Ansible

You can also wrap your tasks in a block and put become: yes on the block. So, inside your roles/role_name/tasks/main.yml, you'd do this:

- block:

  - name: Tasks go here as normal
    ...

  become: yes

This will run all the tasks inside the block as root. More details of Ansible's blocks here (latest docs).

I have found a solution, although I think a better solution should be implemented by the Ansible team. Rename main.yml to tasks.yml, and then write the following to main.yml:

---
- { include: tasks.yml, become: yes }

Another solution is to pass the parameter directly in site.yml, but the main idea of the question was reusing the role in other projects without forgetting it needs root:

---
- hosts: localhost
  roles:
    - { role: name, become: yes }