A very basic approach to a dragon roar would be to experiment with a pitched-down human scream (add treble when pitch-shifting), combined with roars from animals such as walruses, lions etc (you can experiment with the pitch on these ones as well).
– David Filskov
I used a plastic patio table, dragged it long and short across the cement, played with the EQ and pitch and got some very interesting roars.
– Miguel Hilao
To get you started with your dragon sound design, you’ll find a sound library with creature sound effects here.