Air dried clay stone walls?

[sakura11]

Hi
I have been given a magnificent samurai castle built using Arden wood a d what looks like plaster covered with paper
I want to build the base into stone
Should I use filler direct and then scribe or air dried clay laid directly on th e structure
Will it peel off a d do I need to glue oe fix it somehow?
28mm size
Many thanks

[Norm]

Air Dry Clay does shrink as it dries, so do a test piece first if going down that route.