Absolutely, especially if the building has exact clones of your apartment without a terrace. When running comparables within the building, the terrace feature will add additional value. Agreeing with Lynn, it cannot be included in the total square footage, but can be added as a unique feature.
Remember, you know what you purchased the apartment for and based the equivalent comparables and the natural increase in value of your property, price it accordingly if you plan on selling your unit.
The increase in price of your Condo is undetermined, until you set up an appointment with a experienced real estate salesperson, or an appraiser that will appraise your property, properly. Be cautious of anyone who will give you a price for your property without doing the proper research to back up the claim.