Hey, dragons are afraid of fire too sometimes!
It's really awkward since they tend to start spitting fire when they freak out from fire they see around them...
The build really looks too simplistic mate.
Make a large castle or like some large terrain build with caves or something.
That is more likely a build for a TDM.
I once hosted a TDM with an edited version of that one desert castle default build.
It was a really simple edit but it was quite fun to play with.
In short, i expanded the land around it with some baseplates.
Planted some tree bricks, surrounded the land by cube mountains and invisible high walls (to prevent dragons from flying away) a little bit.
I also made a cubic cave where the dragons spawned.
The thing is, you can keep it simple, but you need to do a lot better then that. ;)