I think I have the answer to your question. First you add all things you want to build with this unit to this unit in the unit editor. Then you create a trigger which make the buildings unaviable to build. For example like this:

Initialization
The loop make that by all player between 1 and 12 this buildings are unavailable.
After this trigger you have to create a second trigger which makes the buildings again available. So that you can build them if your skill of your ability is higher. For example like this:

Skill
I hope I helped you.