According to
this table you can both use Liadh or Lorn Rann.
But I don't think that the world of Esteren would be grateful enough to the PCs to grant them access to these old arts, especially if they are forgotten as they are told in the Book 1 - Universe.
Anyway, I can try to "create" an ogham.
Let's try, following the table.
I'd like to create an ogham that generates fire. Ok, let's try it.
Fire is a nature force that can destroy everything, and many things with low power. Means that it's strong.
I'll probably set the difficulty to a high point.
It's an ogham, so we'll use the columns "Scale", "Persistency", in my opinion. (depending of how you use the table...
The "Scale" may be for the distance between the Demorthèn and the Ogham to be able to communicate. Of course, to be easy to call, the ogham should be in the hand, or worn as a necklace or something. Ok, I'm a gentle GL and my PC is a powerful Demorthèn, so I let him try to make an ogham able to be called from 5 yards.
The "Persistency" may be for the time the Ogham will keep its power. Then, an ogham "must" be available for LONG time. If it's for at least 1 day, it's going to cost much. Then, it's gonna be a 5th circle ogham to create.
For the 5yd, cost of 5 rindath and 2 rounds of casting.
And for 1 day of existence, 20 rindath cost and 5 rounds of summonning time.
It makes a DC of 25 and a total 25 rindath cost, and 7 rounds of casting to make it.
Ok, it's raw and not well-established, but it's a form of use...
