I played a lot of campaigns, I`m an avid consumer, but I don`t think I played one covering the Troll Wars and very few campaigns with Trolls.
I guess it will not be huge but you can have a general story about the Warsong prior to leaving, the exodus itself and what happened before they meet with Thrall in the Barrens.
With a bit of imagination you can make this a great campaign.
In mission one you eliberate one concentration camp while Thrall is eliberating another.It can include base building or not.
In mission two you can have the Warsong assist the rest of the Horde who assaults Durnholde.Base building present.
In mission 3 you assault an Alliance base to get ships, Thrall is doing the same to other naval bases.Base building present.
Have an interlude that has Thrall elaborating Grom - to link it with the real story.
In mission 4 you land ahead of Thrall since you don`t crush but you still have to fight Quillboars and Centaurs to link up with all your men..err i mean orcs. No base building.
In mission 5 you are moving ahead with your clan - guard mission, fighting raids etc. NO base building.
In mission 6 you come across two Alliance bases who block your path into the Barrens.Base building - big show down.
This is just an example of what your could do.
Good for training up your skills.