All that you have to do is post an idea, that can be strictly Lord of the Rings, or it can be a little bit of a mix of Lord of the Rings, and something else. I'll use mine as an example:
It would not be pure LotR, rather, it'd have medieval Europe and Asia as well, just to add a little twist.
Factions I'd get from our world would be (from europe) the English and the French. From Asia, I'd have Sengoku Japan and the Three Kingdoms era of China
There'd have three camapigns, one for Lord of the Rings and one for the Mediaeval Earth. The third would be a special campaign combining the two groups.
I'd also probably eliminate uber powerful superpowers (ie, Earthquake or Balrog) for the factions of Middle Earth. I'd probably not have 'Evil Campaigns', but rather have the player choose their side at the beginning of each battle, also for a little twist.
The fations of Earth would each have the same basics, but they'd have three elites that no one else had, like the Japanese would have Samurai, Ronin, and Shogun. Seige would be have an increased role, but would take longer to train and would also cost more.
Heroes would be a little more powerful than an equivalent standard unit (ie, Aragorn = swordsman) and would have different/new powers. From Earth, I'd use famous leaders, like Talbot and Joan of Arc for Europe, Oda Nobunaga (Japan) and Cao Cao (China) for Asia.
Cavalry would be more powerful, as they were the 'tanks' of Medieval lands.
No base building, bases would be prebuilt with anything needed.
Large amount of resources at the beginning of a battle, resource gathering would be limited.
As a counter to that, unit buildtimes and cost would reflect their skill and equipment.
Terrain would provide more bonuses.
Basic units would be in hordes (5-10), whereas elites would be single or small (2-4 soldier) hordes.
I'd have a combo horde system, for upto two units in any combo. (2 basic Hordes, 2 elite hordes, 1 elite and 1 basic horde