I have acne scars on my face and pitted skin. My dermatologist recs derma roller?

Maybe. For deeper pitted acne scars, you will need something with significant effectiveness is resurfacing the skin. This would be either dermabrasion, a surgical procedure requiring either local or general anesthesia; or co2 laser skin resurfacing, possibly more than once. The derma roller will have very minimal benefit for significant acne pit scars.
Depends. A variety of approaches are necessary to improve not remove acne scars. Specific therapy is dependent on the type of scars and skin type. Potential therapies include subcision, cross tca, medical roll cit, dermabrasion, laser and other treatments, including prp.