[Ragnarok-X]

Well i think this quite important:

When writing "designcreation" files, you must follow a certain order. Put the advanced ships at the top, and low-tech ships at the bottom, the AI will always build the ships at the top, so given you put advanced ships at the bottom of the file, the AI may design them (for example battleships), but it actually will never build them, because it thinks that the "escort" the top is more advanced.

My 2 cent, which took me a LONG time to figure out.