Buildings

[Flying Pig]

Is it possible to add completely new building trees, like gymnasia or city extensions? If so how?

[Aradan]

The Complete EDB Guide (https://forums.totalwar.org/vb/showthread.php?t=50439)
Most info on how to do things is already available to modders in Scriptorium, so have a quick look there before asking. Modding Answers subforum has everything categorised too, to amke things even easier.