Parts needed would depend on version built. There are at least 2 of them: old epic and epic armageddon.
Both not identical. So which stormhammer should it be?
Some different aproaches to built a stormhammer are out there, 4x guns in 2 turrets may be the common accepted take.
And standard baneblade turret doesn't fit twice at a standard chassis
So: 1x baneblade + plasticcard + plastic putty + tubes (plastic or metal).