Attic is an empty space inside the roof. It is used for storage of things that are used occasionally. No one wants to live in altillo o desván. If your flat is an aticó which is a very pleasant to live in, with fresh air and a wonderful view over the city or the beach, you can call it PENTHOUSE. Loft is more or less synonym of attic but it is now a very fashionable for a large space that has been converted for living in. It´s used in Spanish with this meaning.
(Image below is “aticó” for the Spanish)