Is having a roman nose a sign of having deviated septum? What are the signs of deviation? Sometimes I hear a 'shh' sound while I'm breathing, is that?

Septorhinoplasty. You need to have your nose examined. Be sure your surgeon is a board certified facial plastic surgeon with expertise in nasal procedures.
No. The primary reason for fixing a deviated septum is nasal obstruction. If you are concerned, see an ENT or facial plastic surgeon.
See picture. A roman nose is typically an overly rotated nose with a prominent hump and slightly downward projection of the tip. It is usually more visible from a side view whereas a deviated septum is more commonly seen from the front and is caused by the midline of nose deviating to one side or being twisted. It may cause obstruction as the primary symptom but may also bleed or adhere to the turbinates.
Deviated septum. A deviated septum may or may not cause significant difficulty breathing through your nose. It can also manifest externally with a twisted external appearance. The sound that you are hearing may be related to nasal obstruction from multiple causes. A whistling sound can also be related to a perforation in the septum.